My boyfriend's best friend is trying to get with me?

My boyfriend and I have been dating for about 8 months now. Everything's great but I think his best friend is crushing on me or at least want to fuck me.
he's been full on trying to flirt with me the moment he first met me when my boyfriend introduced me to him.
I tried to tell my boyfriend that it makes me uncomfortable but he says his best friend is always like that and is just joking around (they've known each other since kids).
Problem is that I think his best friend is kind of the pack leader type, and my boyfriend never ever tries to anger him or tell him he's wrong or disagree with anything he says.
Problem now is that his best friend has been getting even more touchy than usual, sometimes he slaps my ass and he likes to get close and whisper sweet nothings in my ear. He's tried to kiss me several times before when my boyfriend wasn't in the room but I managed to avoid. And sometimes he puts his hand on my thigh, and he's told me he's feeling horny. I've told him to stop about a thousand times but he just won't, I've even slapped him, but he just laughed. He's even said things like 'you me in my bed right now, I won't tell'
Its hard to avoid him cause he shares the house with my boyfriend.
I don't know what to do, I love my boyfriend and he's great in all areas apart from the fact that he won't speak up, I wouldn't even be surprised if he let his friend kiss me and do nothing about it.
What should I do? Why is he doing this to me? Is it like a power thing?
My boyfriend's best friend is trying to get with me?
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