Sent a rejection message to girl who was still in a relationship. She hasn't responded. Am I the bad guy?

[boltnrun]

My ex's niece did things like that ALL THE TIME. She had a boyfriend she lived with but still messaged other guys, flirted with them and chased them and even sent them lingerie and bikini pics. She just really craved attention from guys and didn't care who she hurt in order to get it. She had any number of guys on a string. She told them all she loved them and was only with her boyfriend "for now". She didn't mean a word of it. 

You don't need to hang your head if you run into her back home. She's the one who was cheating and you put a stop to it when you found out.

[JoyfulCompany]

You did the right thing, absolutely. And good for you!

As to future encounters - act polite (i.e. say "hi" if unavoidable) but distant and undisturbed. You don't need to avoid a favourite place because of her. It will make you move on faster if you're able to desensitize towards her and not make it a bigger deal than it is.

If you were in a long and committed RS and you needed a lot of healing, I wouldn't advice exposure right away but I think under the circumstances, you'll be alright eventually.

You'll find someone better and actually available. Good luck.