humans are territorial so of course guys/girls get jealous, the more important question is to what percentage of jealousy is that matters. I personally don't pay too much mind if my girl talks to other guys, I had my ex's talk to guys all the time and I won't ever tell them who they can't befriend or talk to.
If a guy flirts with her, I trust her to do the right thing and tell him to stop. She's a grown woman to take care of herself and her little problems, ill only step in if he gets too physical or weird.
Not always, the guy I like, his best friends are girls... And he's ALWAYS out with them or whatever...it doesn't bother me much though.. It's his life, he can be friends, go out, talk with whoever he wants..