If you watched any early episode of Cheers, you had to wonder why those two were dating. As a Wikipedia contributor notes:
Though bright and witty, Diane Chambers was also often pretentious, snobbish and woefully lacking in street-smarts.
And what would a down-to-earth guy like Sam Malone want with someone like that? If you have to ask, you’ve probably never been a guy:
I once saw Shelley Long at the Sherman Oaks Galleria. I think. I can’t be sure. I was too busy turning away to make sure I wasn’t staring. Which tells you far more about me than it does about Shelley Long, but such is life.