Thinking of confessing

I’ve been friends with him for almost four years, and I’ve developed a crush on him. It’s gotten to the point where I cannot stop thinking about him and it’s getting tiring. When we first met, he confessed and we almost dated, but he felt it wouldn’t work and called it off (it lowkey hurt) but I wasn’t able to move on from that. We became really close friends and I feel like I can truly be myself around him. He’s given me mixed signals (one time my friends say they saw him blushing when he was looking at me, his eyes light up and he smiles when talking to me) but I also believe he doesn’t have any feelings for me (most notably he sent me a reel which said ‘send this to her for national sisters day’ which kinda makes me rethink confessing him). I really do want to do that at the very least I can get rejected and move on, but I’m also scared losing him as a friend. I really do cherish him as a friend, but I cannot let my feelings continue to fester and end up regretting not saying anything. I’m thinking of writing it on a letter and giving it to him next time I see him. Any advice is appreciated, I hope I’m doing the right thing.