<human>: So last year, me (23) and my GF (22) of almost 5 years split up for around 3 months (mostly due to me being a bit of an asshole at the time). Prior to this, and during this time, my best friend (23) and I became distant. He was good friends with us both.

Eventually, myself and my GF got back together. I moved into a house with my friend and another buddy, until due to conflict between the friends, by best friend moved out, losing contact with us all (there were other factors involved in this).

Shortly after this, it was revealed to be that during the short time my GF and I were apart, she and my friend slept together. This happened once, during a time when she was undergoing treatment for depression.

Obviously, I wanted nothing to do with him whatsoever. My GF and I worked through it, and are now engaged. I know people will say I shouldn't have forgiven her, but I look at it from the view that we weren't together, so what she chose to do was nothing to do with me. The part that hurt the most was my friend's betrayal.

Now, almost a year later, other friends who he fell out with at the same time have gotten back in contact with him, and he now works in the same building as my GF.
I can't decide between getting in touch with him to bury the whole thing and move on past all the negativity, or keeping my distance. Part of me wants to move on past the whole thing, but at the same time the betrayal still stings.

Can you summarize the given text in a few sentences?
<bot>: my GF slept with my former best friend when we were briefly separated, and now I can't decide to forgive him or not. Me and the GF are still together.