Da Rock,
I want to share something that my husband and I learned in couples' counseling that made a HUGE difference in our relationship and you can try it on to see if it fits.
When we started couples' counseling, one of the things that we learned is that we both carried a belief system that said there was some rational, impartial scale of behavior that what we wanted and what the other person wanted could be measured against. Whomever fit the scale better "won" and the conflict was therefore the other person's fault and their responsibility to fix. I think I might hear this in your query about how much expressiveness is OK to ask for.
When we acted like this, we ended up in a blame game, and would have endless circular arguments about what the standard was and who was right and who was wrong. This proved to be a disastrous waste of energy and time (didn't stop us from trying it for years. It also made our arguments look like the Daytona 500: around and around the same track.
)
We had to learn two important things. The first is that we didn't need justification for our feelings. Feelings just are and it's ok to express them and what we want. (This was the easier part because it frees you up, you do know the harder part is coming.) The second part is that since there was no need of justification, then there also was not some impartial standard that we were supposed to achieve. Just two people, both of whom had needs and desires and the point of our discussions was to express our needs, listen to the other person and come up with a compromise we could both live with.
So, you're girlfriend is doing NOTHING wrong by not being as expressive. You are doing NOTHING wrong by wanting more expressiveness. (Sit with that for awhile, I found it very uncomfortable in the beginning. Something in me kept insisting that ONE of us must be wrong.) So it's ok for you to ask for more expressiveness. Your girlfriend might be able to change what's she's doing such that it reassures you. Or maybe she's not willing to do that and you have to decide if this level of expressiveness is something you can live with. It's about expressing your needs and owning your own feelings and letting the other person do the same. Then you have to balance the tension all human beings have to which is the fight between our wanting total independence so that we can do what we want to do versus our need for connectedness and considering another person's feelings and needs to achieve that connectedness.
So you're not looking for the RIGHT solution, you're looking for the solution that works for you and her, one that allows both of you to feel comfortable. (If you don't feel comfortable with the solution, resentment builds up). And only the two of you can figure out what that looks like for you. Being as honest as possible and being willing to listen to the other person non-defensively really helps.
AG