constantly wondering why

Ok, so to start of, I was dating this one guy throughout high school and ended the relationship a week or two in to college. We were so close to making it to 3 years. However we ended it because we were having too many problems and I was having too many trust issues. (I should add that we go to different colleges) We ended on bad terms because we got in a huge argument and completely stopped talking for about 2 weeks. After that we talked and apologized to each other and what not. However he said he wasn't ready to be in a relationship which I thought was kind of stupid considering the fact we were dating for almost 3 years. I let him have his time and space but in that time that we were broken up we would talk here and there and eventually hook up once in a while. Fast forward to the present, we officially started talking again about a month ago and o asked him what type of things he did while we were broken up. He never wanted to tell me but he eventually did and said he made out with a couple of girls and never went further than grabbing ass and boobs. I don't know what to do or think. I know he did these things while we were broken up yet it still bothers me to think he's capable of doing that. He says he's sure he won't do anything anymore. He said he's serious about us now but I'm constantly wondering why he would even do that..am I not good enough? Should i trust him?