Why am I still trying to control him?

I was with my (ex) boyfriend for 8 months and I do love him but I wasn't mentally mature enough for a full on relationship, we lived together for 6 months I worked from half 8 to half 4 everyday while he done nothing. So let's get to the point, I broke up with him which he didn't understand and constantly texted me asking if we was to get back together, I was talking to an old friend of mine who he didn't like (wasn't allowed to talk to other boys) and he started. But now I'm so interested to see who his been talking to and meeting. His 18 and his attitude to girls work anything is so bad, when we first got together who would talk to about 12 girls not even in a friend matter he wouldn't care about hiding it. Well from my point of view it was a bit to friendly, and I know his meeting other girls that I know off but why do I want to know so bad?