Never will, either.
I just don't believe it's something to do.
I think cheating happens for a reason- usually the offending partner feels like s/he is missing something.
I don't feel like I'm missing anything with my SO. If I do, I talk to him about it. He's wonderful, and even when he pisses me off or we go through a rocky patch, there's nobody I'd rather be with.
If at any time I'm discontent with the relationship or think there's something "better" for me, I'd break it off.
BUT to be perfectly honest, I don't think it'll happen. I'm with the man I fully intend to marry.