I'm no longer single myself, but I spent many years single and have faced this question more than once.
What I found over the years of being single was that if two people didn't share their Christian beliefs, there was way too much pressure regarding sex. The sex question is always going to be a hard one, and if one of the two isn't living under God's principles it's even harder.
Then there is always the issue that, for the Christian, marriage should be the goal of dating someone. And, if one is dating someone with the idea of marrying that person, and that person isn't a Christian, one must grapple with the issue of how the kids are going to be raised. No matter how much someone might say, "If you want to raise the kids with your beliefs, OK....it's really not going to be OK. All parents who love their children will naturally want to impart their heartfelt beliefs to them. It's very difficult to raise your children to believe "a" about God and have your spouse come along and say, "b"....usually, the kids just wind up having either no beliefs or weak beliefs...usually (not always).
My hubby and I weren't on the same page when it came to God, but we were within the same book so to speak....he believed in God, he just didn't have any kind of personal relationship with God. However, he did want the kids to be baptized and raised in the Christian faith, so that was huge. Over time, he did indeed develop a very strong personal relationship with Christ. BUT don't ever underestimate how hard it is and how much pressure it will put on the relationship.