Relationships

I'm not a pro at this...and the past few weeks my mind has been a battlefield. By personal experience and watching Christian relationships first hand I have seen a lot of crap go on and be justified just because its a "Christian relationship". I am struggling. Let me digress:

I was in a Christian relationship and we would push the envelope regarding our boundaries (not just physical) but I never felt convicted. I think it was because we both had God in our hearts. We talked about everything; our struggles and our desires. We would both fall into temptation but I think there was a peace about it because typically we would both ask for forgiveness. Now being in a relationship with a non-Christian I struggle a lot internally. I watch my actions closer and the second I begin justifying things the battle begins. I don't feel okay with things. I am holding myself to a higher standard but the frustrating part about it, and what I don't understand is..why am I doing it now that he doesn't follow Christ? I didn't seem to care much about it until after the fact when I was in a Christian relationship, but now its all thats on my mind.

I don't get it.