She will give up on me just because her family doesn't want me

I have been in a three-year relationship; we were thinking about getting engaged, but her mother has never liked me, she’s always been quite cold. The other day, I heard that she has been putting ideas in his head, saying that I’m not good enough for him and so on. Now he seems to be acting very conflicted towards me; he has changed, even his voice sounds different. I’m really scared that he would leave me for his family. Honestly, after putting in so much effort, going through something like this feels really heavy.