I (24M) am in love with my bestfriend (23F) and I don't know what to do

So to protect the innocent let's call my friend Abby. Abby and I have been friends since highschool (2013) and I haven't had a crush on her since about 3 years ago. Maybe there were some slight feelings but nothing concrete. About 6 months ago I did ask her out. Abby didn't want to go out specifically because we have too many mutual friends. I told her I understood and felt extremely heart broken. I told her I needed time to heal. So I took 2 months to shake it off. I came back and I felt like I was prepared to just be friends. Flash forward to now and I still feel the same way. Maybe even stronger. I just think about we a true friend she is to me, and how much we just... click. We just know how to cheer each other up and make each other laugh. She's brings color to my life whenever I see her. I really do love her.

I feel like I need to stop seeing her. These feeling only keep growing and I just don't know what to do. I'm thinking about just letting her go all together. Maybe that "If you love her, let her go" thing should apply here. But I also feel like no one is ever going to compete with how well we know each other. And I don't want to ruin the friendship just because I can't stop loving her.

What should I do?

TLDR: I'm in love with my best friend and I have no clue how to proceed