As for how to communicate, use "I" statements and talk about the specifics of what you do want rather than making vague statements about what you don't want.
Don't say "When you do x you make me feel y". Instead say "I felt y when x happened". The first blames them for making you feel something, the second just tells them how you feel about it but doesn't blame them for it. It's a fine distinction, but it can stop them becoming defensive and shutting down.
Ask for what you need and/or want and make sure they do the same. You all need to remember, though, that asking for something doesn't oblige the other person to agree. That goes as much for them asking things of you as it does for you asking things of them. If your wants are fundamentally incompatible then you need to decide for yourself if the positives outweigh the negatives and what you're going to do about it. Being "just the girlfriend" doesn't mean you have to be a doormat.