You know, even if that's how a succubus works, if you're uncomfortable with the situation, you're entirely within your right to say I'm not okay with this

Except they didn't. They had their character say they didn't want to get married and that another character should object at the wedding!

the DM was forcing his player how to react to what was happening, which has zero justification.

Well... yeah... that's kinda how a succubus works?

It seems like you're just here to be a dick to the op and question everything, for no reason.

I was pretty clear about the reason, actually: they said they don't remember the details of how they got to that point. The details of how you got to that point is what changes "that's unfortunate" to "what a shitty person". Without those, there's nothing.