I have a coworker in my department who is a pretty decent individual. He has been dating a girl in our company who works in another department. He is completely obsessed with her and thinks the relationship is great. She, however, thinks he is a complete idiot and openly bad mouths him, but she likes being spoiled and I get the impression, he's the kind of safety net for her.

My question is should I tell the guy out of respect for his feelings or wait until the gossip comes around and mind my own business?