<human>: I recently split with my BF of five years because I was extremely suspicous of his behaviour. He cheated in the past and was giving me a lot of reasons to still be suspicious (being overly close to one of his gay friends, being very distant from me, etc.)

I was still in the process of moving out when I woke up one night to hear him having sex with someone in our bedroom (I was in the spare room). They were trying to be quiet but I heard everything. I didn't burst in, just knocked on the door and asked if what I thought was happening really was. He was really defiant and said he could do what he wants, so I immediately packed a bag and left for a friend's house while they were still doing it. I just wanted to get out so I didn't make too much of a scene.

I was devastated, because I still loved him, but don't know if I do now. I'm just really confused. To hear the person you love and have just broken up with do that is one of the most upsetting things that's ever happened to me. I take monogamy a lot more seriously than he ever has. Technically it wasn't cheating, but it almost seemed worse as I actually heard it happen.

The next day he called and said he was extremely sorry, he knows what he did was nuts and completely inappropriate while I was still in the house, but now he really wants to get back together. I just don't understand how someone could do that, it's extremely cruel. I know it probably sounds a bit mad but I'm still not sure if I want to get back with him or if I'm setting myself up for more suspicion and heartache, or if I should just cut ties forever. I don't know if anyone else here has ever experienced such a thing but I just don't understand why he'd do that. Technically he could do what he wanted as we've broken up, but why do it right under my nose?

Can you summarize the given text in a few sentences?
<bot>: Ex slept with someone while I was still in the house, now feels really bad and wants to get back together, but I don't understand his behaviour and am scared it's a bad idea.