Sex surely does complicate relationships. It seems that we invest too much in the way of perceived ownership rights in lovers. Maybe that's just another view of the problem of jealousy or exclusivity. There's nothing inherently wrong with physical intimacy in its own right, or as natural part of a friendship relationship. It's when the exclusivity or ownership issues arise that things get complicated. All of us are different in the way we experience such things, and I suspect that most of us find it difficult to supress those "ownership" notions. There's a time element there as well. At the end of the day, if the relationship isn't a satisfying one, then the only intelligent option is to move on. That doesn't mean that anyone failed, etc., etc., just that the match wasn't right.