Late to the party but here goes:

I dated a coworker for over a year, and we were both friends with the other 20+ employees. Amazing for the first nine months, then she started pulling the "not now > right now, too much > not enough" game, so I ended it, in person. All nice and composed, she was okay, I was relieved. I told her I wouldn't make it awkward at work and would just act like we never had a relationship.

For the next six months she quietly tried to get me fired by various methods, managed to have my shifts changed twice (for the worse), made all the female employees afraid to work with me alone (this hurt the most), and when I followed her shift, ensured she left some kind of mess (physical or otherwise) that I'd spend half my shift fixing.

I took it on the chin for six months, never once saying a bad word to anybody - they were friends with both of us, so it wasn't fair to do that to them. Then woke up one morning and decided it had been long enough, I was going to give my notice and look for another job.

I get a phone call the next day from one of the only friends I had left there saying my ex had put her notice in, and was moving to the other side of the country in two weeks.

As a kicker, they threw her a farewell and she made sure I was invited. A few ex-staff came along, who were still friendly with me, and one told me afterward they came along only because there was some plan to accuse me of something in front of everybody and blame me for her being "forced to leave". They refused to ever tell me what it was, so I can only imagine it wasn't nice.

tl:dr If you're going to date crazy, don't pick one you work with.