Can you sue your exes new partner because he was cheating on you with her and lost out on a £4000.00 holiday as a result of it?

No if this was the case the courts would be floodgated with this nonsense.

The woman isn't to blame your ex is because he had the option to not cheat but he did. So don't be mad at the woman point the finger at him.

Also it seems like he has moved on so maybe you shouldn't waste anymore energy on this but instead follow his lead and do the same.

Karma will take care of it , and you get to keep your dignity.

Sue the ex!!

It is a matter of law. Unless you are married, a girlfriend and boyfriend have NO legal obligation towards each other. Chalk this up as plain old crappy luck. Karma, like Friend said, will handle it in the end though...

Sadly, no. It would make for an interesting case and Maury episode