I'd definitely agree with Skip here.
Though, he's right, and sex can be the #1 thing that breaks up relationships right after you begin... and if you're feeling guilty about it, well, then that's another way for it to be bad.
Though, at twenty, I don't think it would be a good time to get married anyway, regardless of how long you've known him (2.5 years isn't bad, but it's not that long). The rate of divorce is what, 50%? And the younger you are, the higher it is. Nobody goes into a loving marriage thinking they'll ever get divorced, but it definitely happens... everyone thinks they know better. Not sure why that is. 'Course, I'm younger than you are and definitely not thinking about marriage, but it's true.