HELP! I'm in a long term relationship but I think I'm falling for one of my friends..

First, I want to thank everyone in advance for taking the time to read this post. I know it's a lot but I want to give as much detail as possible.(but not over killing it) Also I apologize for any grammar issues. So I'm going to try to explain this the best I can. Let me go ahead and give a little back story to this current situation. I've had the same best friends since I was 16 and I'm 26 now. They are all straight men. I'm just going to make up names for them for this. Let's say they names are Nolan, Eddie, Ryan, and Dex. It's great because they fully accepted me since day one and didn't' treat me any different because I'm gay. We've been through a lot the past ten years and are there for each other and we're all basically brothers. Now three years ago is when things started to get weird. My boyfriend and I at the time had just broken up and it was a pretty bad break up. About two days after the breakup Ryan and Dex were able to convince me for them to take me out. So we were having a good time but then I started talking about my break up and with alcohol involved it wasn't pretty. They tried to cheer me up so we decided to go to Ryan's house and just hang out there. It was fun and I was feeling better. We started drinking again and Ryan and Dex were cheering me up and it was all great. Dex ended up leaving because he had to go to work the next day so it was just me and Ryan now. So we just continued to hang out and to put it bluntly the next thing I knew we were making out with each other. Pretty passionately might I add. I don't remember who initiated but we were both equally into it. Then the next thing I knew we were both completely naked and basically started to have sex. Both oral and anal. It wasn't just me giving we were both equally receiving and giving. Keep in mind I was extremely vulnerable at this time and it was good to feel wanted sexually and I didn't care if it was by one of my best friends. To make matters worse he had a girlfriend at the time who totally didn't deserve this. As selfish as it sounds though all I cared about was that I was feeling wanted and it felt great. The next morning I woke up and realized what had happened. He was still sleeping so I hurried up and got dressed and basically ran out of the house. I walked all the way home and I felt so ashamed and confused. One of my best friends for years who I thought was straight as can be had sex with me. So I get home and shower and try to understand what had happened. Later that day I get a text from Ryan stating, "hey man where are you why did you leave?" I replied with, "I'm sorry man after last night I'm so confused and didn't know what to do" he then replied with "oh yeah, sorry about that" and that was it. So that just confused me even more. Exactly one week later we all took a trip to the beach, including Ryan's girlfriend. It was like nothing ever happened but inside it was killing me. Within that week I started to develop feelings for Ryan which had never happened before. I knew it was because I was still in a vulnerable state and what had happened between ryan and me, during that time, made me feel great. It was killing me that I couldn't talk to anyone about it and I really needed to. A couple days later I was at Nolan's and his girlfriend Jackie's apartment. I figure if I could talk to anyone it would be them. Nolan was the first I came out to and was there for me since day one during that stage in my life. It took a lot for me to tell them for I was scared they wouldn't believe me or for they would tell everyone else. So I eventually did and we actually talked about everything that happened and I was starting to feel relieved and they actually believed me. So they advised me basically that I'm developing feelings for him for being in a vulnerable state but try not to take all the blame because Ryan knew what he was doing as well. Later down the road eventually the rest of the group found out (Eddie and Dex). I knew Eddie was because of me (drunken confession) and Dex was because of Ryan. After everyone found out things started to shift. We all started to hang out less and less. I would hang out with Nolan and Eddie more and Dex and Ryan would hang out with each other more. Ryan even went to as far as blocking me on Facebook. But when we would all get together it was like none of the awkwardness existed and like nothing happened. After awhile Ryan moved his girlfriend down here from South Carolina (Ryan was stationed there for the marines) and they got a place together. Everything started to die down (awkwardness) and things were going back to normal. I no longer had those feelings for Ryan. He still had me blocked on Facebook but I really didn't care. Fast forward a year later I meet my current boyfriend, Tom. I fell in love with him and we've been together for a little over two years now and have a place and everything. He's great and everyone loves him. By this time everything was back to normal for the most part. We all still hung out but couldn't as much with all of our current jobs and conflicting schedules. This past weekend we were all hanging out and having a blast. It was like we were all in high school again. Towards the end of the night Some of us came back to mine and Tom's place. We stayed up having a great time. Then the next thing I knew it was just me, Tom and Ryan. (Ryan's girlfriend had just moved back to South Carolina to finish one semester of school, they are still a together) Also, Tom was informed what had happened in the past between me and Ryan when Tom and I first got together. While us three were hanging out, out of nowhere I started to feel annoyed and pretty angry about how everything went down. So I was pretty balsy and just came out with it. I basically told him how shitty things went down and why the hell would he do that. I wasn't trying to play victim or anything but I was mad that I was so confused. I told him I at least wanted an answer. Also told him how shitty and childish it was that he blocked me on Facebook. After I got it all out he basically had a break down. He kept apologizing and kept saying he knows it was shitty how he handled it but he was confused himself and didn't know what to do. He just kept apologizing and it scared him that there's a strong chance he might not be straight. He was on the brink of tears and I kind of felt sorry for him. I guess it's because I didn't' think how it was really affecting him. I didn't know what else to do so I started to comfort him and he let me in and we started hugging. The next thing I knew we started lightly kissing each other, Right in front of Tom! I then realized what had happened and stopped and felt shitty of what we've just did in front of Tom. I then told Ryan it's best we call it a night so I showed him the guest bedroom and that was that. I apologized to Tom and I couldn't believe what had happened. He caught me by surprise because he told me that I needed that off my chest and the kiss thing was because we were both really drunk. After talking about it a little more Tom and I went to bed. The next morning Ryan and I were talking like nothing happened last night and he went on his way. Now as my week is starting I'm starting to find those same feelings I felt three years ago about Ryan. Like really bad. I know I shouldn't and I'm basically back in the same situation. I love Tom and I love how we are all back to being brothers again like we used to (me, Nolan, eddie, dex and ryan). Now I'm starting to feel like I'm falling for Ryan again. I don't get why because I'm in an awesome relationship with a great guy. We are all planning to hang out again this weekend so I guess I'm nervous. I don't want these feelings to continue to grow and I also don't want things to get awkward again and I want us to stay brothers like we are now and used to be. I guess what I'm asking is what should I do? Again, thank you so much for taking the time and reading this entire post but I wanted to give as much detail possible and it feels good actually getting this out.