I'm having a sleepover and I don't want my moms boyfriend to sleepover too.
Why? Will he cause problems?
I hate him.
If it isn't your house, unfortunately you won't have any say-so. I also wouldn't expect your mother to put much stock into your wishes.
I'll tell her to kick him out before I leave.
You can tell her but you might not get what you want. Your mom should be able to live her own life without you trying to control hers or expecting her life to revolve around yours.