I wholly agree with Jeaston. Especially if you are considering a friendship that has lasted for a long time vs a recent (compared to the friendship) relationship. One logical reasoning is that since a couple, liking/loving each other and all, would often find each other more important then even their long time friends. So lets say since you care about your girl so much, you decided to sacrifice your friends. But friends are there for you when the girlfriend cannot. There is no guarantee that you and your girlfriend will be together forever. Thus, if unfortunately that were too happen, and you come back into the single life, but you lost all your lady friends for the sake of this relationship, then you have nobody. I know a lot of people who have made that "mistake" (quotations because some people would disagree), but I don't think anything would feel more lonely or guilty at that point then losing your girl, and finding out you ditched out on your friends for her sake.
I don't think anybody is worth keeping if they can't trust you, friend or girlfriend. I would not be so dishonorable to suddenly decide to forget and ditch those who have been with me through thick and thin, whom I've shared memories with, just for the sake of even my would be girlfriend's jealousy.
Sorry if I seem kind of angry here, I have lost many so called friends and felt utterly used and left back just so that they can continue on their little relationship in the past. Many of them broke up too, only I refused to not be around like a lap dog to comfort them when they are on the rebound.
Gl with your decision sir. Hope things turn out for the best.