Most can't stomach my methods because of their self esteem...
I do want to say though, that she is probably having an affair with the married guy at work. This would make sense to her saying she would still go on vacation with you. When a woman has an affair with a married man, she usually won't leave her home if the man doesn't leave his wife. He has probably told her he was going to leave, but can't yet because of the kids or some other lamebrain excuse that women fall for.
So, instead of going on vacation alone, she gets you to tag along as her puppy. Still hoping she would want you back.
I know you don't want to hear this, but the best way to get them back is to bring another woman into the picture. Works great, works fast and usually straightens them out for good. She won't be breaking up with you wanting to be "friends" ever again. You already allowed her to do it once. Now this is twice..
First time.. Shame on her .. This time shame on you.
Look.. Get some backbone. Get some confidence... Let her think you are over her and are EXCITED about the new dating world that is out there for YOU.... Works like a charm. Better than hanging around hoping, and moping and being all faithful and in chech while she eats all the cake.