Read the replies, our members have suggested you plenty of good suggestion. But lets face the reality, if you are private assistant to the boss of the firm, the HR wont hear your complain. The only people who will be interested is Police which is after effect, meaning when the damage is done. What you can do before that is leave this place.
What is your priority in life, to earn more or to live a dignified life? If you chose money, this remaining scared will follow you, once the damage is done, money wnt buy the reputation. If you chose dignity, then leave the job and settle for a decent place. But its very clear, you cant have both of them.
Adding with that, I hardly have seen any private sexretary or confidential assistant who have not been in someway molested by the boss. Either consenting sex, or forced sex, or non penetrative fondling or online harrasment. The job is going on for years where a lot of girls love the extra money and ends up as a mistress of the boss. Having a great relation with the boss's wife doesnot help, as a wife mostly knows her man's nature. If he is exposed, the wife will stand beside him saying the secretary is a whore who lured the man. Thats to save the marriage.
So whatever you do, its your priority and call. I can get to smell something is coming on the way, he is just measuing you how soon and how far he will drag this. When someone gets a pay which is not appropriate for the job, there has to be some problem under the carpet, that will come out in right time.
I know a few prestigeous institute where the top exec floor in office turns to a bar and free sex place after the office hour. Those girls are willing to be a part of these and they accept because they know they get paid double of their pay for this pleasuring top management. A lot of these girls are married, and the husband also knows how extra money in mid of the month comes. The bad part is, these girls if resist the advanced, they are fired from office and given with such bad recommandation, that getting a job in the same city is impossible.
Do tell us what's your priority and what have you deided..