Sarge pretty much has a point... in situations like this, the problem doesn't lie within you, or the girl you're speaking to, the problem is with the boyfriend, because if he has issues with his girlfriend talking to other men, then he clearly has trust issues, and trust is one of the major foundations of a healthy relationship: if he doesn't trust his girlfriend to let her talk with other guys, then there's bound to be problems with that relationship.
Heck, just to give you guys an example, you all know MrsPepper and I are bestest buddies, and have been for several years... well, she's engaged, and you know what? Her fiancee is perfectly fine with our friendship, and even thinks its an admirable one at that.
Matter of fact, I read an article about these kinds of situations not too long ago, and yes, I know there are some concerns that there may end up being WHEN HARRY MET SALLY types of scenarios, but the main thing is, there shouldn't be any jealous from a significant other over your best friend, or any of your friends for that matter, being of the opposite sex. Of course, there are still some measure that should be taken into consideration to help keep any motives of jealousy at bay, such as treating your relationship with your significant other more important than your friendship with someone of the opposite sex, but what it all boils down to is trust.