People are so weird. I once worked closely with a single woman, and the boss had a big Christmas party for the managers, and she brought a guy that she'd been dating for a couple months, and was getting close to.
For some reason that none of us ever learned, he decided to completely ignore her that night. He knew nobody at that party but her, and yet he pretended like he'd never seen her before. It wasn't a big party,maybe 20 people, so we ALL saw what was going on. Eventually, he took her home, but they never went out again.
I asked her about what happened, and he wouldn't discuss it. He dropped her off at home, and they never spoke about it on the ride home or after. The guy just decided to turn into a different person that night.
BTW, she was a really cool person, pretty, fashionable, great hair, super smart, funny, great job, owned her own house, etc. The loss was entirely his.