What is his thinking? Why? My fault?

don't want to make this too long but I am miserable and don't know what to do! I need male and female points of view. I keep blaming myself.

My ex and I had been together for over 3 years. I found out he was cheating a year ago, August 2014. It was the most devastating event in my life. Two mutual friends finally told me because they felt so bad. Not only did he cheat, but it was an affair. Apparently him and this girl were together for 3 months, had sex, talked all the time, and she was in his school program. I think the hardest part was that it wasn't like we were unhappy.We weren't going through a "rough patch" or anything. We practically lived together and were best friends. It shocked me that I barely saw any signs.I truly felt I would marry this man. I broke up with him after I found out because he wouldn't confess. After a while he came begging back and seemed genuinely sorry, cried to me (something he had never done), admitted everything, called me non-stop, texted me non-stop, told me this girl meant nothing, begged for a second chance. I told him I didn't think we could be together again, yet we continued to slowly hang out again, spend the night with each other, talk and text all day. Slowly I started to think I could give him another chance but wanted to be patient and not jump back in. I looked for signs he changed. He was still talking to this girl in his school program and I would confront him but he said it was "just friends". I believed it, He was trying so hard to spend anytime with me, and literally being more open then ever. We slowly fell back into relationship without the actual title. Then one night when we were hanging out (still "technically" broken up) I saw a message pop on his phone from this same girl saying "I had an awesome time this weekend, the sex was amazing." That previous weekend I had gone home to visit my family, the ONE weekend we hadn't seen each other. I was again devastated. He told me he only hung with her because he thought we would never get back together and he didn't know it was his "actual second chance"and he would never speak to her again if he knew we could get back together. I blamed myself and was again devastated. It was my fault because we were not "official"? I got a job in another state to get away and said I was too hurt to consider anything. But I loved him too much and slowly he began working his way back in my life....calling constantly, asking for anytime we could have regardless of what it would mean.

The two months before I moved once again we hung out constantly. He showed me the text of how he cut her out. I said we shouldn't be long distance but before I left we hung out all the time. I moved away for my new job and we still continued to talk constantly and I made 3 visits out to see him. HE was so attentive, once again no official title but called each other several times a week, texted, "good morning" and "good night" texts. I began to once again think we could do this because I loved him so much and he still wanted to try. I never brought up the past. I went to visit him this last time and kept saying we should try to be long distance. He vaguely said he should. The night before I was supposed to leave he left in the car and as I was picking music a text popped up from this SAME girl saying, "I miss you so much". I went into the messages and they talked all the time and he was telling her he missed her so much and "hey babe" and I also saw messages with two other random girls. I was again devastated. I did not even confront him about it and left the next day because I didn't feel like arguing or lies. But why did he tell me he cut her out? How can she mean nothing and they are STILL talking? Why does he keep texting, calling, telling me he loves me and wants me to move with him if he is still talking to all these girls?

Is this my fault? Why am I never good enough? I love this man so much it hurts so I wonder if I told him I would be willing to completely let it all go and get back together would he finally drop this girl and others. I know we were not technically together but how could he continue telling me I am all he wants but then still be talking to all these girls? I could never. I am so lost and hurt and broken....Can we be saved?