Hello!

I am desperately seeking some advice, so glad I found this website. 

My SO's son, who is 16, is probably the most disrespectful kid I have ever encountered.  We have been together for 4 years, and I am a lot closer with my SO's 2 daughters who are 9 and 13, than I am with his son. I bend over backwards for his kids (while caring for my own 2 daughters) and I feel like it's never enough. He has recently brought drugs and paraphernalia into out home, drinking, has all E's in school, no job, and treats everyone in the home like dirt, except his dad. I am the only one who says anything when I see or hear him being disrespectful to his sisters or if he leaves a mess (like always) I am the one who "bitches" about it. The other day, his sister told me that he was making fun of and mocking me, saying that "My cooking sucks becuase I use jarred pasta sauce, and that I need to be in the kitchen and make him a Mother Fu**ing sandwich, and that his dad needs to put me in my place otherwise he will get his mom to". I was APPAULED to say the least to hear he was speaking this way about me. I told his father about it, and all he said was "I'll talk to him". No punishment, didn't take anything away from him, NOTHING. Now I have to walk on eggshells in my own home and I guess I can'at cook pasta anymore beuase my jarred sauce isnt up to par for him. I feel like my SO is so desperate to have a relationship with his only son, that he puts me on the back burner and lets him slide with everything. (His son has left before and went to live with his Maternal grandfather who spoils him and lets him do anythign he wants). If either of his daughters acted that way or were failing in school, he would take EVERYTHING from them. I am really trying my best to hold my tongue, but after hearing about what he was saying about me this last time, I have so much anger and want to yell and scream and "tell him about himself", but I am the adult and I don't want to stoop to that level. I dont know what to do. Any advice would be appreciated or if anyone has been in a similar situation please share. Thank you!