Listen, if your boyfriend didn't say anything then you shouldn't bring it up. You can't prevent what other guys talk about around your boyfriend, but the fact that your boyfriend didn't join in is very good. Some females have the saying look don't touch. I personally don't like it when my husband would look, and I told him that it made me feel bad. My husband doesn't do it in front of me, and he actually looks away from a pretty girl. I'm not saying he doesn't check one out when I'm not there, and you know what fine, just not when he is with me.
it's good you trust him...guys talk about other girls alot...doesn't mean that they are emotionally attached to them in anyway. I think what you should do is sit him down and just talk it out. If you know hes not cheating on you or done anything wrong, don't blame in for anything...just talk it out, let him get an understanding on how you feel. He may not be aware on how uncomfortable it makes you feel. Communication and trust are the biggies in relationship. you have the trust part down...now go communicate!