Unsure what do to

So I'm seeing this guy. I kinda knew him years ago. Just reconnected a few weeks back. He's so so nice and kind. Constantly telling me I'm beautiful and just a kind person. We have a ton in common. I really really like him.

Anyway. One of my best friends is mad because she wanted a chance with him but she's in a relationship so it's sketchy of her. At least in my eyes. I told her I was seeing him and she's hurt that I'd do that because she wanted a chance and she feels he was an Asshole because he was telling her he wasn't available. Whether or not that was an excuse or not, I don't know. But it shouldn't matter.

She has a boyfriend so it's weird and I think it's not right to be mad.

I really like him and we're unofficially a couple. But I want them to be okay with each other. I really like him, as I've said and if he's gonna be my boyfriend, I think my best friend should deal with this or not be my friend. Thoughts?