MY GIRLFRIEND WANTS A 3SOME

dear celebrity inc
My girlfriend wants a threesome with either two females or two males. What should i do?
The thing is, i really love this girl and one of her fantasies is to have a threesome with either two girls or two guys. I found out that she is bi-curious, and I'm scared that if we have a threesome with two girls, that she would take off with the girl, and leave me. Also, i do not want a threesome with two guys, cause im not bisexual or anything and im not about to sit there and let another guy pound my girlfriend right in front of me. If i do, i have concerns that, what if he is better than me in sex? or what if she likes it too much that she wants that for now on. Or if going back to one on one sex is not fulfilling to her anymore, then what am i suppose to do? I just need help, cause she is my real first love and i don't want to mess our relationship up over this

HI M.
RELATIONSHIP IS ALL ABOUT SHARING UNDERSTANDING AND COMMUNICATION, SO I SUGGEST YOU BOTH TALK SOME MORE ABOUT THIS AND TRY MEETING EACH OTHER HALF WAY.
YOU NEVER COULD TELL DOING THIS MIGHT BREAK OR BRING YOU CLOSER BUT IF YOU REALLY LOVE HER AS YOU SAY IM SURE EVERYTHING WILL WORK OUT FOR YOU AND HER