<human>: Background story: My S.O. [25m]and I[24]have been together almost 3 years, with one break up only lasting from the beginning of June to the end of August. Now...the initial cause of us breaking up was my infidelity. 

Save the "you're horrible" shit, that's not the point. We remained close friends through out our break.. I saw one person, the person I cheated with, and he wasn't able to move on yet. Well...my (ex) best friend and roommate started talking to him behind my back..and lied when I would confront her. I know because he told me everything. And we even set it up to get her to leave him alone cause she couldn't take the hint. 

They hung out a few times to my knowledge and few times unknown. I was against this because K(her) knew I still had feelings for him, I knew she was going to do to him as she had done to me..which was lie steal and use him. Anyways, I had a feeling the one time I knew they hung out that something had happened and I was lied to by both of them. But finally, I asked once more and she was honest with me. I was raged but it subsided over a few days. Well a few days later more truth has come out. 

At that point, seeing how badly it hurt me showed me how much I cared and still loved him so. We decided to make things work. Not try, but do. We had a long heartfelt conversation and had decided to not bring it up anymore. That we could not allow our past to effect our future. Now that was in August. Being now, the end of October...I have just about completely forgot about the whole thing regarding him and her. Today he tells me that he still hates his self and how much he hurt me and broke promises. I dunno how to assure him that there's no need to dwell on it. We're getting married in a week and I really do not want to go into our marriage with this...baggage.

Can you summarize the given text in a few sentences?
<bot>: I had an affair, we split, found out stuff about him and my best friend, we're soon to be wed. But our forgive and forget isn't working on his self. :(