Girl Problems (yes, again) Please help?

Right, so the girl I was crushin on who so kindly broke my heart keeps getting mad at me whenever I even mention another girl. It's pretty rare that I'm ever home for the night since I prefer crashin out at a friends place. More often than not these friends are girls. We sleep together in the same bed (I am, after all, the only one not living with my parents) but thats it. It's purely platonic, I just like bein able to wake up next to someone other than my dog in the morning. Strangely enough she gets mad when she asks where I am and I say "At Abby's" or "At Nikkis". Then the next day she gives me the cold shoulder and gets even madder if I ask after her new dude. Anyone wanna help me figure out what the hell her problem is?