Stepson

My partner has an 18 year old son, he is lazy, rude, violent and abusive. It is not only me who thinks this, his Grandad thinks the same.
He has thrown a pint glass at me sworn at me including telling me to **** off called me a pr**k etc.
I have lent him money, given him lifts to his friends, helped him with his school work, helped fix his bike etc. But still he is a nightmare to be around. His attitude causes a horrible atmosphere at home and I am at my wits end with the situation.