You MUST not show ANY jealousy around her. NONE AT ALL, women hate jealous men and need to feel that they are justed by the ones they care about. She is going to probably test you, many WAS do this.
Just have fun, and don't focus on just her. Go out and have a good time with everyone there, even this guy you don't trust. At this point your GF and you are Freinds, and you have to treat the sitch as such. I know it will be hard, but friends wouldn't get jealous so you have to not be.
If needed find a distraction technique to use if you start to feel jealous. Make it so no one would notice it. Remember you outward expressions can give you away. If you believe nothing is going on with them, then do and think "as if" there is nothing going on and they are just close friends. Or even better yet, think to yourself that he is just her long lost brother.
Don't know if this will help, but you do know what you must do. Enjoy yourself, and leave the sitch thoughts and discussions her on the DB BB.
God Bless You,
Reuben
Cautiously hopeful and keeping the Momentum
