I'm going to lie to my housemate
What sort of lie are you going to tell?
I don't want him to go out with me this weekend.
I think it'd be better if you just told him the truth.  What is he finds out you were lying lateR?  You'll be living with someone who's angry with you then.
WTF, lying is fine and also I can't be with him 24/7, it's my freetime.
I know it's your free time, but you should still just tell him that you don't want to go out with him.