Do you think I should admit to my girlfriend that I don't have much faith in our relationship?
Hm, why do you think the relationship is going to fail?
Because she talks about premarital sex all the time
At least you are being honest with her. It would be a whole lot worse if you lied about it.
It's a fucking sex life it's not fucking rocket science.
OK. Well, being honest about your relationship issues will benefit you in the long run.