Don't know what to do

Ca

I'm 23 weeks pregnant and engaged to a guy who has a 4 year old from a previous relationship. His son is very rude and disrespectful to me and so is his son's mother. My fiance doesn't do anything about it. Lets his ex talk shit about me, lets his son be rude and disrespectful to me. I don't know what to do anymore. It's to the point where I don't wanna be around them anymore its gotten so bad. Any suggestions or advice on what I should do?