Ending a Friendship: Should I or Shouldn't I?

How do I end a friendship? Should I? I was going on dates with a neurotypical guy. We were talking about being official, but then, suddenly without warning, he listed a lot of problems that I never knew we had and said we should be friends. I told him that we could always work through them since most of them were simple/small issues and we should at least try to talk about them. Instead, he then said he's not over his ex, which is understandable, so I agreed to be friends. However, now that we're friends and he's gotten more comfortable, I'm learning he's not a very good person. Also, 3 days after ending it with me, he started having s3x with and dating another girl (to be fair, I'm also dating someone else). What confuses me is how, when it comes to me, he's not over his ex, but for her, he is. However, even ignoring that, I'm learning he's not a very good person. I do have a lot of fun talking to him and hanging out with him though. Should I stop being friends with him? Can I stay friends with him and just not be very close to him? If I should end it, do I tell him we aren't friends anymore, or just slowly fade away? Is there a way this can be fixed that I'm not seeing?