I don't know how to fix my relationship

My fiancé and I have a one year old son together and are coming up on our 3 year anniversary. As many people change after they have children, we both changed in ways. Before my son was born I was a musician and lived an extremely wild life. I had more friends than I could care to count, spent all night out, and did whatever I wanted. I met my fiancé, and we were together for a short time before she got pregnant. We both partied in that time and it was a blast. She quit when she got pregnant, I didn't. I still cared more about my music and my own selfish needs than my budding family. I cheated on her and deceived her while she was early in her pregnancy, and for about a month and a half we were apart. In that time, I continued to live my life how I wanted until I finally hit rock bottom and was left with nothing. In my time of need, after not speaking, and despite everything that had happened she had no hesitation to drop everything that she was doing and come to my side. We moved back in together the following day. At first things were still rocky, I had stopped the cheating, but I continued to go out with my friends and drinking however much I wanted to. Eventually she told me it had to stop and if I wanted to be with her i needed to change and they did. I got myself a real job that can support my family, cut out the negative people in my life, and I made my family and work top priority. My son was born and for over a year now she's been a stay at home mom (she has been looking for a job for some time now) and I have been a full time contractor. I have been faithful to her, open with her, and try give her and my son as much as I can. Things have had their ups and downs as any relationship has but nothing major has happened, we haven't until recently yelled or fought in any way like we did in the beginning. There is now a huge problem in our relationship that apparently has been a problem for a while but was never addressed to me. My fiancé has been distant and is upset because she feels like my life revolves around nothing but her and that I am suffocating her. If thats what I am doing I don't mean to be at all. She says that I am boring now, and that I no longer seem like the person she fell in love with. Now I have changed. I don't do much anymore out side of work, I have very few friends outside, don't go out to the bars and drink, and I don't dress the same. I shave every day now, I started wearing ties, blazers, and nice shoes. I want to look and feel appropriate while I'm out with her and my son, especially with my profession. I am extremely happy with who I am now, Id much rather go to the park on my free time and read a book, play poker, or go play a round of golf with the guys at work than go out and drink. She says that I am acting like a 30-40 year old when I should be enjoying being 22. She goes out until 2-3am every Wednesday to her favorite bar by herself and I stay home with the baby, which I have no problem with. Every time she's ever went out until lately she's always back 2-3 am. I don't tell her that she cant do anything, if she's asks about something and it bothers me I will be open and tell her but the choice has always been hers. I just cant understand why she feels smothered by me not wanting to go out. Its not as if I don't offer to go out with her (id love to go have fun with her a night that we can find a sitter but she says that her nights out are her alone time and I can respect that) Im happy being at home watching a movie or reading a book. Thats relaxing to me, it doesn't seem right that I don't judge her on her nights out that she wants to go drink. Im not hurting her or myself by being by myself. And its not like we don't go out and do things together, we go on vacations, we have weekly dinners out, we see concerts, movies and comedians here and there. When things are good they are great. She says a big part of it is that she is stuck at home all day and never gets a break since I am always working. I tell her over and over that id love nothing more than to be home to help her but I cant do that and work at the same time but she seems to blame me. For a while everytime she asked me to stay home from work I would but my boss now is fed up with it and my job is in jeopardy over it. About a month ago she met this guy, her new "best friend". She doesn't have many female friends, I very rarely have a problem at all with any over her guy friends. They started talking on Facebook and it was innocent at first. In a couple days it graduated to texting, again I had no issue. But then the texts were more frequent to being all day and all night, she started locking her phone and deleting messages. As any person would I started to get paranoid and suspicious. She invited him over to our place one day while i was at my christmas party, I came home to him drinking beers on my couch. She introduced us, and instead of getting upset I tried to get to know him and believe that this wasn't going to be an issue. He seemed like a decent guy, going through a divorce with two kids and a musician himself. I backed off a bit. Then on christmas she went to his house until 2 in the morning without telling me, gave him a christmas present though she never got me anything. the following day, our sons birthday, she did the exact same thing but this time ignored all my calls and texts and stayed at his place until 630 in the morning. she came home and flipped out on me for being upset, saying that it is her right to be able to go have friends and that she will not be with anyone that tries to control her. a week goes by and she starts getting bitter with me about everything, constantly putting me down and ignoring me all together. she got distant and started talking to him more. for the past three weeks she's either told me she was going to his house for an hour and came back at 6 in the morning or has lied to me about where she's going, went to his house, and came home at 6 in the morning. the time before the last I told her that i couldn't and wouldn't do this anymore and she agreed that what she was doing was wrong. she told me that she wanted to work on getting us back together. so last week we finally got approved on a house, and she went out to his place again, came home and told me she kissed him. she broke down and says she wants to fix things with us and that she was wrong. I didn't even yell at her, i broke down a bit, and we talked for hours about everything. She said that she kissed him and he didn't kiss her back, she said that she's confused because she loves me but she feels like she can be herself and have fun with him. she says she doesn't have feelings for him and never has. she said she was just confused and instantly regretted it. She blocked him on her cell phone and said he was gone and that things would change. 3 days later I saw them snap chatting and i lost it. she then flipped on me saying that she made the mistake, not him, and that she doesn't need to ruin a friendship over something that she did one time out of weakness. I told her I can understand that but I want to work on our problems first and to give this time to heal. She still talks to him regardless of my feelings and gets so angry if I even mention it. On top of that, our mutual friend told me that she came to her 2 weeks ago and said she had kissed him. My fiancé says thats a lie, she swore on our childs life that this was the only time but I cant think of any reason why our friend would lie. I asked her if I could talk to this guy, if he really is only interested in friendship I want to trust him too but she won't let me without threatening to leave. Im just wrecked with paranoia now, I want to believe that they only kissed once and that it never went further but all signs call me stupid for thinking thats the truth. I want to believe that every time she goes out to do something with her friends she's not really going to be with him but I cant. I want to move on from this and heal. I had a past, I messed up far worse than she did but I don't know how with him still in the picture. Its all I can think about when he texts her phone. I sit here tonight as she is out at a "surprise birthday party" for her friend, and I cant help but to fear she won't come home again and will be with him. What do I do? Ive tried talking to her about it, and every we do things usually look great. She is remorseful and acknowledges things are going wrong. She makes all these promises to me in the most sincere way, seems so genuine. She even said that she wants to get married this year and conceive another baby in the spring. But within 2 days one of her friends invites her out and I'm back stuck watching the baby so she can have fun and If I ever complain or tell her I'm tired she will literally throw a fit about how much i control her and how she's given up so much and does so much for me. but i pay for everything, i treat her to everything, include her in everything. I cook, I clean, I tell her how beautiful she is every day. She tells me i'm everything to her, that i'm a great father, and that she couldn't imagine a life without me in it. Within 30 minutes and 1 year olds temper tantrum I am back to being "the bane of her existence". She tells me she wants us to work and that she is 100% invested into this relationship. I want the same. But I am afraid she's just going to continue this behavior. I sign papers for our new house tomorrow, its significantly more than what I am paying now and cant afford to take days off because she came home an hour before I have to leave for work. She promises that things will change. I want to believe that she will change as I did but I am so scared. She says her biggest issue is that I have no friends and don't want to go out unless its without her. I want to understand that but I truly am happy with the little friends that I have and my little activities that I enjoy (reading, cards, golf, paintball, ect.). If i'm going to go out to the bar its going to be with her, I have no desire at all to go drink because the only time I have fun drinking is when we drink together. she's my best friend, but I give her her space to be with friends . I don't understand whats wrong with me. I don't want to push her into the arms of anyone else again and smother her. But I also don't want to go out to a bar alone to meet people like she wants me to do because I won't have fun. I have fun how things are now. I get every joy I need in my sons smile when we play, sing, and watch movies. I get every joy I need when I wake up to her beautiful face and come home from work to her kiss. I get my joy in working a full week and being able to take my fiance out to a great dinner and treat her to a night full of wine, massages and cuddles. She seems so happy most of the time. Then out of nowhere hell breaks loose and Im awful again. I love her more than anything and the unsettling feeling of deception and the fights is destroying me. thank you to anyone for reading this whole thing, if anyone did, but everyone just tells me to leave her and that i don't deserve this. I cant imagine not seeing my son every day, I cant imagine her not by my side anymore. I want this to work and she says she does. but how do I trust her? How do I fix this? I feel like I am doing everything right but nothing seems to get better. I cant live like this anymore, but I don't know how to live without my family. somebody help me and give me advice. I need it.