Hey Pandas, How Do You Break Up With Someone?

I made this post because I (13F) myself need advice on how to break up with a guy (13M). First, I'll give som context:

We've known each other since we were six years old and we've always been kind of frenemies. In 6th grade, I realized that I had a crush on him. We started chatting and sending each other memes about random stuff. Two days before summer break, I confessed to him that I had feelings for him. He told me he felt the same and we got together. During summer break we met up several times and took a walk, same route every time and it was really awkward (you know, teenage love). Slowly, I felt my feelings for him fading away but I still didn't break up since I hoped the feelings would come back. They didn't. When we started 7th grade, our whole class was split up and so were we. We go to different sections of school and since then we have barely talked and met.

The past months or so, I realized I actually had feelings for my best friend (13F). She's an amazing person but makes me feel really nervous. In order to see if something could happen between me and my friend, I feel that I need to break it off with my boyfriend. He's an incredible person, awkward but a gentleman and he said he has been crushing on me since 3rd grade. It just adds to my guilt and I just don't know how to handle this. Feel free to post your advice on how I should proceed, in both breaking up and what I should do with my friend situation.

I should also add that both her and my other friend know I'm bisexual, although my parents don't. I've already told my other friend also about this crush but I feel that I need extra advice :)

Thank you for reading all of this, I know it was a lot of text but I needed to vent