You may find that, sexually, you're rather incompatible. In fact, this incompatibility may extend outside the sexual realm; you feel it from the beginning in a strange lack of feeling between you -- as if you're underwhelmed when you're together, though you both want to feel bigger and better sensations. Physically and emotionally, you might just go through the motions together instead of ever feeling anything truly genuine and overwhelming.
You tend to derive a lot of emotional sustenance from your sex life, but that doesn't happen easily in this relationship, which is tough for you to handle. Don't misunderstand -- if your relationship is progressing, you both want to interact on a level that affects you both in a big and satisfying way. But somehow, you keep misdirecting yourselves and eluding each other. Admitting that you're not connecting as well as you'd like to is the first step; the next step is talking openly and honestly about how each of you is feeling in the relationship, and what you'd like to feel. Compromise is crucial to keeping the relationship going, if that's what you both want -- but it is possible to learn to please each other, physically and emotionally. A closer connection between the two (your bodies and your hearts) helps, and you can make that connection through communication, patience and persistence.