<human>: Can you summarize the given text in a few sentences?

My friend of many many years recently had sex with my girlfriend.

I don't know all the details, but I know alcohol was involved. I know she drinks quite often, sadly I've been trying to work on that with her. I've known her my whole life and I've known him since middle school. Its a pretty difficult situation and I'm not planning on removing them from my life. Everyones called me crazy for it, but I just can't say goodbye to the people I love most. She came out and told me first thing. I read her texts, and I saw they both regretted it. I didn't snoop to find them, I just asked if I could see it real quick. I feel like I can forgive, I just don't know how I should move on and remove the subject entirely. I don't want to choose between the two and I've cared about both of them for far to long to throw it all away over something stupid. 

1. This happened a few days ago
2. I can't blame anyone in particular, they're both at fault.
3. Drinking was involved.
4. He lied to me about it and denied it the night it happened.
5. I'm lost on how I can move on from it, and put it behind all of us without it coming up.
6. I haven't even had sex with her yet.
7. She and I are still dating, but he and I are not talking.
<bot>: Best friend of many many years had sex with my new girlfriend whom I have known since birth. They both regret it and I don't know how to move on.