Need Advice

Please tell me if I’m wrong but my fiancé and his mom have a weird relationship to me. She will walk around butt ass naked in front of him or even in her underwear and he will occasionally do the same! When I say something about it or if I tell him to put clothes on he tells me I’m stupid bcuz that’s his family but when they are alone I get this weird feeling! And it pisses me off when he works a 10 hr shift and goes straight to his moms house first and mind you we have children together! Need advice she even works at her house in no bra and a tank that you can see everything so she might as well not have a shirt on at all ! Am I overreacting ?