The GMC exists for a reason. Please, please, please atop worrying about getting him in trouble with them. Most often, unfortunately, they take no action, so your concern is misplaced.
However, this man is coercive and manipulative, and manages to turn your socialised ‘niceness’ against you. This is a man who is also capable of being inappropriate with patients. If he gets into any trouble with the GMC, it will be because someone else has also reported something before.
I think it is irresponsible to not speak up. I also think all your feelings of guilt are misplaced. You haven’t caused his appalling behaviour. -he has. He would have behaved the same way however gently you ended it.
You deserve better op, and so do all the other women he will treat like this in the future. Does it help to know that whatever trouble he might encounter because of you reporting this to HR, in very honest term, without minimising anything, is you showing solidarity with other young women, colleagues or patients, that will come across him in the future?
It makes me very uncomfortable to think this man is treating patients, he is unhinged and his sense of entitlement is dangerous. Reporting his behaviour honestly and fully to HR seems like safeguarding of patients and colleagues to me.
Rooting for you OP, hope the meeting goes well.