Why am I so protective of my Ex-Boyfriend?

I dated a guy for a couple years (It was long distance so the majority of the time we weren't together) and we went on and off some summers. He visits for 1-3 weeks in the summer, and it would basically be like a summer fling that we tried to continue when he left but it never really worked.

Anyways, I got myself a new boyfriend who I have been dating for 2 years. My Ex, his brother, my boyfriend and I all hang out together and we all have fun..

BUT, my ex has been getting into some bad stuff and hanging out with people I hate in the summer. Recently he's started smoking pot, and is ravenous over it. He's been telling me (proudly) how he cheats on girls and how he likes to date younger girls. He tells me about all his sexual endeavors, and I know most of them are most likely fake.

(he told me he got road head *which was the first time he got head* and he DIDNT ***.... thats a little suspect)

Anyways, I'm really protective of him. I want to grab him by the shoulders and tell him to cut it out. He's doing terrible in school and is not going to get into a good college. He's going down a bad path. Also now he's going on summer flings with all the odd girls I don't like. I keep having talks with him and telling him that he needs to stop and think about his future..

Why do I even care? Is he doing some of these things to make me jealous? Or is he jealous of where I am at now?