I (23M) have developed feelings for one of my best friends (22F) and have no idea whether to tell her or not

I’ve been friends with J for at least 6 years now. We met in high school when she dated one of my mutual friends, but after they broke up within a month we stayed in touch. Over the years our friendship grew and we’ve become very close friends. We both love the same things and spend hours discussing house of the dragon, Star Wars, or trying new food pop ups through our city. She’s been there for me through multiple breakups, and I did the same for her. When she went to college hours away we would still talk on the phone for hours, watch movies online together, and see each other whenever she was back home. When I was deployed she would always write to me, send me packages, and make me feel less homesick. I had a recent breakup and I realized I was doing something I never noticed about myself, but I couldn’t help compare how I felt about my ex to how I felt about J, and I realized that I did have feelings for this person. She’s moving back from college in a few months and moving to the city where I live where I currently study, we’ve already planned out a whole bunch of things we’re going to do when she comes back. I feel like I need to tell her how I feel, but am scared of losing someone I hold so dear to my heart. Any advice would be greatly appreciated.

Tl;dr: have feelings for my friend of 6 years, scared of telling her and possibly disrupting our friendship