Trust and communication is the key. My ex used to be very jealous and that just didn't fly too well as most of my friends are male. Jealousy turned into a control thing and that is just something I will not tolerate.
When you care very deeply for someone it's hard not to get jealous over them, at least it is for me, but it is one of the "bad" emotions as far as I'm concerned. If I am with someone I love then that means I trust them 100% so I give them all the freedom they wish and as long as the respect/trust I give is returned then there is never ever any problem.
And...the best thing to do if you ever get jealous if some girl hits on your guy when you are out, just wander over and whisper in his ear what you want to do to him when you get home. See how quickly your "nemesis" ends up out of the picture!
