He has no ground to ask for anything he's given you back, unless it was agreed between the two of you that it was a loan. Especially any money that he paid you for any overnights etc because you were working and he has bought a service.
If he knows your real name and is threatening to out you, you can go to the police, call 101 for advice. I've been told in the past by a DLO that if someone outs you without your permission then they are committing an offence. I'm afraid I am not sure which one, but I have been assured that it is something that will not be taken lightly, if that is the route you want to go down.
I hope you get sorted as this sounds rather nightmareish, best of luck x