Nightmare 3 year marriage with step kids. Help please

Hi, been married 3 years, both second time around. My wife is English. I'm in northern Ireland where we are living. When we got married my wife came over here and brought her 27 year old son to live with us with the understanding he would stay 1 year maximum. Anyway it's been a disaster with me not getting on with him. He is still here and he's now 30. I moved out for a couple of days a few months ago telling my wife he had to go but she won't put him out. I'm really at the end of the road with this. I have no kids myself and I'm suffering depression with the atmosphere in the house. My just keeps saying she is caught in the middle. Has anybody got any advice? Should i split up and let the two of them live happily on their own? Cheers Steve

No he is not special needs. Just a lazy bone idle lay about. Does a part time job. Says he has no money all the time. My wife needs to choose him or me. I had arranged before that he was to be out by 15th September. Now my wife says she doesn't remember the conversation!! Think she likes having him in the house but I'm afraid i cant stand him.