No, you did NOT overreact, and no it was NOT right or okay for him to continue after you told him to stop.
What you do from here is really up to you, and whatever you do that's right for you is going to be okay. I would suggest first talking to your counslor about this, and after that, the choices you have are basically either to have a vvery long talk with your fiance explaining why what he did was NOT okay, and setting very firm limits to assure he doesn't do it again, or you can choose to take a break from him for a while or even sever this entirely. It's really about how you feel about it and again, however that is is okay.
It's very hard to give advice on things like this sometimes because it's difficult to get an idea of what the dynamic in this situation really was, and what your usual dynamic is. Flatly, if it was really scary for you and you were very clear and he was very forceful, you are essentially talking about a sexual assault, and in that case, I can't encourage you enough to examine this and your whole relationship and really give a lot of thought to not being with this person, because sexual assault tends not to be something someone does just once.
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