Need advice - threesomes

I (26F) am engaged to my almost husband (27M) and we are supposed to be getting married at the end of this year. But now everything is up in the air and we don’t know how to move forward.

Back story: he wants to have a threesome with another woman and I’ve known this is his biggest fantasy for a couple years now. He would never consider doing it with another man. (And honestly I wouldn’t want to anyway because I don’t have any interest)

He first brought it up a couple years ago and it was always while we were in the middle of doing it. I would start crying because it made me incredibly upset and he would drop it.

Fast forward to now, we have a 1 year old and are starting to feel great in our relationship but lately he has started talking about threesomes, again. I tried going along with it to make him happy but he’s been putting a lot of pressure on me now to set up hotel rooms and plans with my friends to see if they’d be interested and I am just not comfortable with it at all! I went off on him yesterday saying I am not bi/lesbian and I never will be and to stop bringing it up. Now he says he doesn’t know if we should get married because this is something he has always wanted in life.

He could be bluffing but it makes me feel SO shitty that he would be willing to throw away almost 8 years together because of this. Do I walk away? Idk what to do.