I'm upset with my mom and her new boyfriend because they're having loud sex while I'm home.
Why does your mom and her new boyfriend having sex bother you?
They are too loud for my liking.
It's reasonable to be upset if you hear anyone having sex, especially your parents. It's inappropriate for your mother to have loud sex around anyone, let alone her children. You should explain to your mother how uncomfortable it's making me feel.
Hopefully they will stop.
It's always good to discuss problematic issues. It's better than doing nothing, or just as bad, overreacting in a destructive manner.