Another thing: I think regardless of the situation, as in whether or not it involves religion, if you are continuing to build a relationship with someone that you intend to break off in the future, you are only doing a disservice to the one you allegedly love. It's different if, maybe, you're young and your parents are pressuring you to do one thing that you really don't agree with, and maybe you intend to fight that battle when the time comes. If you, personally, are already set in your convictions, though, it's just wrong. And what is the point?
It's still a tricky topic, though. So many aspects of romantic relationships could be construed as selfish depending on how you look at them.