I ran into a very similar problem in my current relationship. She was a Christian from the get go, and at the time we started dating that was not the case for me. I was lost as could be. And in some ways my worldly ways rubbed off on her. Not something I'm proud of, but being honest.
I came to know the Lord and we've managed to not only work on her relationship with the Lord but mine as well. We read the Bible together and pray together. And attend church together when we're able. (We have a long distance relationship.).
Don't give up on the relationship; Unless as Ugly said, you feel you're not yet ready for a relationship. Make God the center of the relationship. Read together, pray together, attend church together, praise Him together through music, whatever you're able to do.. Do it.
The way I've come to look at it; You should be in love with God enough that there's no way for you to pull her away from Him you can only pull her closer. Granted, I'm not sure how this situation has played over so maybe there's something I'm not seeing.