There are several ways of answering this:
- if you want to stay virgin to keep your superiority, then just stay virgin. It's obviously more important to you than your girlfriend, so just act upon it.
- if you really are assexual (as a sexual orientation), then I think you will quickly break up with your girlfriend, simply because you have incompatible sexual orientations. Hets go out with hets, gays with gays, etc. You can stay together for years, but your relationship will never be fulfilling for both of you.
So basically it's a no brainer: keep your virginity and get ready for the end of your relationship, when she has had enough of it.