Started falling for my friend's best friend

I (25, M) am flatmates with my school friend (25, M). He has a best friend (25, F). They met in first year of college. They were in the same college and I was in a different college. Honestly, they are quite close, and she comes over frequently—sometimes even staying over when it's too late for her to go back. I don’t mind her coming over. In fact, I really like her presence. It’s fun and cheerful, and every time she comes over, it feels like ghar me raunak aa gayi. Otherwise, it's usually just the two of us being busy in our own worlds. But now, I’ve started developing feelings for her. I really like the way I feel when I’m around her. I’ve asked both of them multiple times if there’s anything going on between them, and they’ve always denied it. When I asked him if he likes her, he straight up said no. So I asked him if I could ask her out, but he hasn’t replied yet. It’s been 3 days, and I don’t know what to do. He has been my friend since childhood, a really good friend of mine, but she is such an amazing girl. Her personality, her aura, her intelligence... I’m just amazed. And to top it off, she’s really pretty too.