Am I the only one who thinks that is wrong?

Its not that's its "wrong". But the fact that you will see your best friend with someone you used to date is very unpleasant.

Its not just that... its OK for him to move on but not for me to even hang out with my best guy friend

Its not just that...its ok for him to move on but not for me to even hang out with my best guy friend

You forgot to mention that..

An ex is an EX! End of story, for both of you. Neither of you gets to have a say in what the other one does. If you are still trying to, then you are not over each other, and need to sit down and talk about it.

I am OK with him moving on because I don't want either of us to be miserable but when we talked about it he said that I can't say anything if he finds another girl but I'm not allowed to find anyone else

And you are listening to his silly macho garbage because..

I am not but he runs everyone off since I live with my best friend...

This is certainly an installment story. I wish you could have said it all in one sentence:

"My recent ex is dating my best friend/roommate, and he thinks that's OK, but he thinks he can tell me I can't date anyone."

Tell your supposed best friend AND him that his behavior is immature, unfair, and intolerable, and that if he won't put a stop to it, and if she continues to go along with it, they are both history, out of there, GONE. (If it's her place then you have to move out. If you got the place together, you have a right to certain expectations from her, but you may be the one who has to move to get away from him.)