So I like this girl and I don't know what to do?

Archie🏳️‍🌈 • Gay?, definitely genderqueer, slytherpuff, potterhead 100%
So there is this girl I like and I I've known her for most of my life. Well so she likes this other girl but I've been falling deeper and deeper in well I guess love with her each day. She's my best friend and I don't want to ruin our relationship. What should I do?