I can't offer much in the ways of advices.'ve this is a situation I have no experience of bar one part.

Whilst honesty in a relationship is important, telling the man you want to be with that you can only orgasm to the thought of someone else will not provide you with good foundations, you risk disheartening at best or hurting him and causing him performance anxiety at worst.

Why not give yourself time getting to know him again, hopefully as you do you can start to replace one fantasy with another.

I have no doubt my partner loves me but if I thought he was thinking of someone else as he came, I wld be devastated.

Just a thought.

All the best, good luck.