A little help what would you do?

so there's this guy hes my room mate an when no one is around hes nice as ever to me then when friends come around he treats me like crap plus i take care of his kids an do everything that a house wife would do for him but my cousin who i introduced him to strictly as friends because she like 14 years younger then him she came into the picture he started constantly treating me like crap but still expected me to do everything for him she left an after that i found out they had sex an now he tries to act like i shouldn't be mad what should i do i want to make him realize im still the one here an shes gone an i didn't want to be treated like trash on the side of the road