Feel like I’m being sabatoged by fiancé family

My fiancé and I have been together for 5 years we have had our share of problems recently we have been talking through our past problems more and coming to closer with a lot of the stuff in the past. We got to a point where we were able to talk about it and work through it without being angry at one another. We have been getting along and moving forward. My fiancé’s family and I haven’t always gotten along but have worked towards getting along. Now all of a sudden he has been talking to his family and my fiancé’s entire demeanor has switched all of a sudden the stuff we worked through has been coming up and he’s starting to act different about it. I’m not sure what’s changed but all of a sudden after talking to his family more he’s been different. I’m not sure what to do I asked him and he says he’s fine. Just needed to vent ladies