I have been with my fiancee now for 6 years, we live under the same roof and he does the same thing. I think its because guys are afraid that his friends will like you more than they do him and hes jealous of YOU.. Not jealous of them for their comments about you. Although its certainly annoying that men do this, I also think its normal. As long as he's setting aside time to spend with you I wo worry about it too much. If he starts to cut your time short to spend time with his friends.. Breaking dates etc, then I would talk to him and ask why.
I once had that problem. Turned out he didn't want his friends or their girlfriends slipping up in front of me. But considering the ? (s) you've asked today, could it be he's a bit controlling.
Sounds like a jealousy and control issue. Your boyfriend is insecure and he is going to get worse the longer you stay with him. If he can't trust you, or control you, and won't allow you around his friends, then I'd drop him. Usually a man is proud of his lady and wants to show her off. You better off without this loser. I bet he has made you feel bad in other ways as well about yourself. Get a real man you enjoys your company enough to share it with his friends.
Maybe he doesn't trust his friends or he's insecure. He might think you may hit it off with one of his friends and eventually dump him. Have you given him reason to not trust you?
A lot of boys do this hun, its because they are insecure of themselves, and jealous that you may like his friends more than you. Don't dump him over it! Just speak to him and ask why he is doing it, and that you would never disobey his trust or cheat on him, just tell him it would be nice to spend time with his friends and him, maybe suggest going on a double date if any of his friends have girlfriends, then you will be able to get to know his friends too. :)