Oh my God. Code red, get out right now.
This is terrifying. It’s already a red flag that your fiancé was the only one not to cut contact with his dad (and not only not cut contact but goes to stay with him). But that episode was a cut and run moment. You’ve got to get out.
Normal response would be like, “oh babe are you okay?!” Cold water, burn cream, take you to the urgent care if needed.
I think this was God or the Universe giving you the strongest sign possible to get out.
Also, all abusers apologize and act sweet after. I’m sure his dad probably did too. This guy hasn’t denounced his dad and has had this unacceptable behavior modeled for him. It’s just… you absolutely cannot. You’ve got to tell him that you had a realization after that trip that this isn’t going to work.