I'm going to give my boyfriend an ultimatum
What's behind the ultimatum?
He is so superficial and he can't be faithful for a lifetime.
I think that you should talk out the issues with him. Giving an ultimatum can be seen as forceful and rude. But it also sounds like you two may not be a good match.
I'm throwing his shit outside the house and kicking him out.
Ultimatums don't usually work out well, but your boyfriend doesn't sound very nice if he's not faithful to his partners. You should break up in a mature fashion instead of throwing his stuff out onto the lawn.