Relationships are all about give and take and sometimes doing things that you might not really want to do.
To be sure, if your boyfriend or girlfriend wants you to rob a bank or hurt someone, that's a hard line that shouldn't be crossed. But lighter things like going to a ballet show (my last g/f was REALLY into it...) and trying to enjoy yourself there make a big difference in how a relationship grows.
In your case, sex sits right there on the border. Your girlfriend is probably going nuts thinking she'll eventually unleash the male beast within you. She must be REALLY hot for you if she's stayed this long.
If you feel good about giving her pleasure, I'd say give it a try. If you can have sex with a girl without taking any physical pleasure into account, that says a lot. If you're worried about your virginity... I dunno, try a strap-on?