<human>: Some background info:
My boyfriend and I have been together for nearly 4 years, we live together, share bills together, you get the idea. 

I'm not the best at writing so bare with me. My boyfriend has been acting different than his usual self lately. He has been mean and distant. 

The other day he had a job interview and he wasn't home. I took this opportunity to go onto his computer history (I know this is wrong, but I was suspicious) he has been acting so weird and our sex life has been pretty nonexistent the past few months. I found out that he has been going on hookup subreddits on here. He was on backpage as well. I also saw that he had gone onto kiks website and possibly made one. 

I confronted him about this when he got home from his interview. Of course it was followed by a fight. He said a lot of mean things to me and said how I should trust him more. But how can I trust him if he's doing this kind of stuff? I told him if this is something he wants to do (hookup with people) he needs to tell me so we can end it. 
I don't want him to be sneaking around. 

He tells me he doesn't want to ruin our relationship but often thinks about having sex with other girls. He told me he would rather date me than have meaningless sex with someone he doesn't know. 
I asked why he was going onto these websites, he said he was just curious. He apologized and said he doesn't want us to break up. 

I don't know what to do! I feel kinda heart broken and like I can't trust him any more. Today is his birthday so I have tried to make it a good day for him but I feel pretty broken.

Condense the text into a few key points
<bot>: found out my boyfriend has been going on hookup forums, he apologized but I still feel hurt. I'm not sure what to do.