A couple of the replies mentioned unprotected sex, and i asked him his thoughts on this. He told me it would be up to me but he would be happy to pay me 50% on top of the regular amount if i wanted to on the basis that we both had regular health check ups.
I can't believe you're actually giving him the choice!! At the end of the day he is still a CLIENT/PUNTER, he isn't the one running YOUR business, why are you allowing him so much power/control? I know you said he's willing to pay more, but they ALL say that (all the barebacker desperadoes anyway). I was recently offered ?1000 for a 15 minute booking for JUST unprotected sex. He could have offered me ?1million, I am NOT playing Russian Roulette with my life or health for cash. The discussion should have just been you telling him that unprotected sex is out of the question - END OF.
And no, it's not different if you're only sleeping with him and your husband - as others have said, you have no idea what he's doing with other ladies. When I was younger, the slogan went (something like) "When you have sex with someone, you're having sex with everyone they've ever slept with."
Sadly, by accepting the breast implant money, you initially put yourself in the position of being indebted to a punter, and now that he wants repaying, he already has the upper hand.
I still think 3 months is far too long for a first trial if you're going to go ahead. Start with 1 month, then extend to 3, then 6, then a year, etc.