My adult stepson is ruining my household.?

we have been married almost four years. the boy was raised solely by his father since age 12 and dad let him have way too much control over his life. now he is 23 and still expecting dad to drop everything and do what he wants, when he wants. we have had numerous incidents in the past four years where this man-child comes to our house and starts griping out dad because dad isn't doing to suit him. to add to the problem, the stepson lives in a mobile home in our front yard. my husband will talk about moving him elsewhere from time to time but never takes action on this! the boy has a job but no real responsibility. he makes a truck payment and pays his electric bill but we are paying everything else. he comes over all the time, calls his dad constantly, has no real social life. the constant visits wouldn't be as much of a problem if he didn't have such a bad attitude! he picks fights with his dad, etc. please don't tell me to do things to encourage his social life. he is 23 years old! everytime we have an incident with him things will cool off and he will quit coming over so much for awhile but before you know it he is right back in the pattern of constant disruptions that eventually lead to a blowup of some sort. i am so sick of this and i'm ready to throw in the towel and let him have his daddy back all to himself! please advise!