if you have conversation proof I.e. texts or emails, screen shot them and post so your former gf will see your proof and you can call the chick out at the same time.

If the girlfriend isn't interested in your side now, she never was going to be. You may have dodged a bullet there.

The psycho coworker isn’t what caused your break up. Your now ex just wanted an excuse to get out. If she actually cared she would have at least heard you out. So I mean in a way you owe a thanks to your coworker. She saved you from a possible divorce settlement and child support payments. Plus now you have money you’re not spending on her for yourself. Maybe send your coworker a thank you card?

Now you can work your way out of your co-worker’s friend zone. You did say you rejected her because you have a girlfriend. Well, that issue is moot now.

Were there any witnesses to her asking you out? Wow, that's ridiculous. FYL indeed. It almost makes me wonder if they were in cahoots.

If your gf believes some random coworker over you, you're probably better off.

Not the most trusting relationship by the looks of it. If she dumps you based on someone making a comment with no evidence that is not the sign of a long-term relationship in the making,

Next time dither about it and report her to HR for making you uncomfortable by asking you out despite knowing you have a girlfriend. Though in all honesty, you sounds like you are better off without your now-ex-gf, because that much lack of trust meant either you had a relationship that was super fragile already, or that the incident was just an excuse to dump you.

If you really wanted to, you can sue your coworker for defamation of character.

Wow. Those bonds of loyalty were ultra fragile.