Maybe some good ideas regarding sleeping arrangements will be found in this thread: Sleeping Arrangements and Beds
But it sounds like your issues are deeper than just a sleeping schedule. Sounds like it's time to stand up for yourself and renegotiate. They don't get to make all the rules just because they're married and that's what they're used to. A triad should be 1+1+1, not couple +1. Also sounds like your girlfriend needs to grow up a little bit.