Having a new fatherly figure around the house is tough, but you have to try your best to think of your mom's happiness and at least try to get along with her new boyfriend. One day if you see her boyfriend sitting down watching TV by himself, try to sit down with him and get to know him a little bit. If you absolutely really grow to hate him, and the whole thing doesn't work out for you, I recommend you to keep avoiding him, and just have an acquaintance-like relationship with him. Everybody deserves a chance, you have to remember that.
I hope everything works out for you.
Pm yo, if you wanna talk about things.