What I should do this Christmas with my boyfriend family?

My boyfriend is super connected to his family so when I went to spend Thanksgiving with them last year his dad out of nowhere got super aggressive with me and rude he expelled me from the house and was super mean I thought he would physically attack me or something. My boyfriend watched all that and did nothing with his dad we just left. On that day I wanted to break up with him but he said that his dad have mental illness and he was always like that ( his dad does not works but have a masters) but he never told me anything about that before. After that my boyfriend left me alone for all the holidays since I have no family in this country I was completely alone for all the last year’s holidays after that happened, so basically his dad is mean and I am punished. My boyfriend love for his dad and family is too big even to cover their bad actions. I have not seen his family since then and did not went there also for Thanksgiving this year and since then I am alone we almost broke up several times because of all that. But this year he really wants me to go their for Christmas if I do not go I will be alone again and I also have the feeling that he might propose during it so I don’t know what to do if his dad is mean again we definitely breaking up if my boyfriend once more do nothing to protect me and put his dad in his place.
What I should do this Christmas with my boyfriend family?
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