Just say it's not that you don't like him it's just you don't want a boyfriend right now.
Think of the Paul Simon song. Hop on the Bus, Gus. Make a new plan Stan.
Call the police.
Break up with him.
Get rid of him!
just like you get rid of anyone else... you use a gun
Wait until your mother and her boyfriend are in the room together and ask, 'Are you going to be my new dad?' This should put him in a hot and stressful situation, a perfect start to slowly driving him out.
Introduce yourself to his wife.
Sounds like he/she doesn't like your boyfriend or is afraid of him. Has your boyfriend ever mistreated the cat? If so, get rid of the boyfriend asap!
get rid of the boyfriend and have two guys with benifits. then your not cheating on anyone
get rid of it
Get rid of him.... and fast.
Change the locks