<human>: Can you provide a brief rundown of the text in within 3 sentences?

So on the fourth of July, my best friend asked my sister out. My sister, who is much older than my friends and me, has never really talked to any of my friends. I expected her to say no. She didn't.
Since then, they've been on four or five dates and are officially a couple now.

I'm very close to my friend. To a point where I consider him a brother. I told him from the beginning, I think it's beyond weird that he's doing this with my sister, and that if he ever hurts her, I'll never forgive him. We haven't talked or hung out for a while. I can't. It's too weird for me. Now he's asking for his best friend back and I don't know what to do because I don't have any options. I can't tell him to stop dating her. Thats not my place. But I also can't pretend to be okay with it because I'm really not. He's either my best friend, or my sister's boyfriend. There's no combining the two

I don't know if time will fix this. First of all, we're about to go to college, and she just graduated, so I'm pissed that he'd risk throwing our friendship away over my sister who he's gonna have to break up with for college anyway (and trust me, he will. He's a man-slut and a week before my sister he was bouncing between three other girls)

I don't know what to do
<bot>: My best friend is dating my sister and he wants me to be ok with it so things go back to normal with us but I'm not