Dude your friends are being a pain in the ass, just tell them that you'll try your best to make time for them. They have to grow up and stop being so needy. Try going out with your friends and your girlfriend, let them get to know each other.
Most of my friends are married or in long term relationships but now I have more friends because of the addition of wives and girlfriends into the group and I obviously understand that they need time to themselves. Actually I think I'm the only single person in my group of friends being an ubernerdy otaku incognito :-)