How to confess feelings for a guy friend of 8 years?

Okay so I want to give you guys all the details. I have a guy friend that I’ve been friends with for the last almost 8 years we met when I was 16 or 17 and he was 20 or 21. It was most definitely a meet cute situation. We met at a mall and became instant friends. After a while I had confessed that I had feelings for him he had rejected me in a way that didn’t seem like he did or did not have feelings for me. So that question has been left unanswered. I had always wondered if it was because I was under age at the time. But it was never brought up again because I went away for school and he went into the Navy. I ended up in a relationship for 5 years while still harboring feelings for him. And now I feel like I should bring it up again now that I’m an adult (23). I really don’t want to lose the friendship that I have with him but I feel like I can’t move on if I don’t know if he feels anything for me. He is currently on a mission and I don’t know if I should send him a letter or message him in hopes that he’ll see it whenever he can get service. And if I do either what should I say how should I go about it? I’m really bad at speaking my feelings and I need some guidance…..