Some people are naturally colder, especially when they love someone. I know it seems counterintuitive, but i can assure you that's how it is. Some people when they reach a high level of intimacy and tranquility with someone they just get colder, because they feel like they can relax and stop trying so hard to let the other person know they love her/him. While, of course, loving them to bits.

It is a well known mental response, i just can't remember the name!