OP - I think deducting the time the woman was there is the absolute least I’d expect. This was a pretty gross invasion of your privacy and it’s hard to imagine on the days she was there that he was doing his finest work either side of that time.
I think you have a very reasonable case here for a bigger discount.
And no, it’s not blackmail. Public, factual reviews of your experience are standard. If he wants to avoid that he needs to make you a fair offer and moving forward he needs to become more professional and not abuse the trust of people he’s working for.