Yeah Ive Been with my Boyfriend for almost 3 years he has a child with another woman?

I knew this when we met. Is it wrong of me to hate to deal with the whole baby mama drama? His son is really disrepectful towards me i try my hardest to be nice to him however he likes to name call me ex cow, *****, etc. He really misbehaves when he comes over to my apartment sometimes even kicking my dog when we are in a store he runs around the store like a maniac and wont listen. If i try to correct him my Bf gets mad at me and tells me let him do what he does hes a kid! Several times hes even hit his dad! We were at a wedding 3 days ago and i got yelled at by someone who works on the ship he told me that i should be watchin my son that hes running around like crazy unatained i was speechless i literally started to stutter i believe i swallowed my tongue! My Bf wants me to play a momie role but i cant have any saying in discipling his son i just feel like this is not my responsiblity and to be honest it s to the point that i just really hate being around his son. Anyone with advice