I'm sort of dealing with the same situation as you. My GF isn't afraid of intimate moments, rather she instigates sex just as much as I do, probably more actually. But the best thing I can say from my experience with my GF is to let her know that you love her unconditionally and that you're always there for her and you'll never leave or give up on her (but make sure you mean all of that and that you can handle the ups and downs). The ups and downs, well the downs, are really really tough to say the least, but I would/will never give up on her and I love her no matter what. I try and tell her I'll give her space if that's what's needed, but let her know that I am here whenever she wants to talk. She will usually text/call a few days later and say how much she misses me.
We've had the marriage talks a lot and I'm not sure how far you are in your relationship, but I would marry my GF in a heartbeat and we've been looking at rings the past couple months anyway. She brings up the marriage talk all the time when she's feeling well, but it can change in a day and she'll barely talk to me for a week when she's having a tough time. The best advice I can give is to try and not personalize (lot easier said than done, I know).
Hope this helps.