I know how you feel. I don't like to give advice or talk about myself too much, but maybe you can relate to this. It's my first time sharing this on reddit. Otherwise, just ignore this. I promise I'm not trying to be a self-centered a-hole.
I still remember the first boy I had a crush on, when I was young and even before I accepted I was gay. We hung out together all the time, and one of the hardest things I had to do was put an end to the friendship because I realized strongly that I was living a fantasy in my mind where we would be together forever as more than friends. It was even more difficult because we were still young, and after I cut him out he was hurt and confused about why I didn't want to spend time with him any more. Even worse, I was a target for bullies at the time and didn't have many friends. He was really my only close friend, which may also explain why I managed to fall so deeply in love with him. As I said, we were young, and I remember suddenly the love songs started to make sense.
For seven years, I was in hell. I would say for a good seven years not an hour would go by when I wouldn't think of him. Throughout middle school and high school, whenever I would see him my heart would race. We would still say a friendly hello and so forth, and sometimes he would try to start a conversation about video games, which is what we used to do most when we would hang out. Many nights I lay in bed and cried. I felt like I no longer wanted to live. I felt a mixture of guilt and regret. I remember when he got his first girlfriend. That was an especially difficult time, but it helped me realize it could never be.
Even now as an adult, I think of him a lot. I have seen him once since our high school graduation. My heart started racing even then. I'm happily married to the greatest man ever, but even now as I type this, I feel this deep sorrow. My husband isn't at all like my friend, which is good. I love him for who he is, not because he reminds me of my friend. That's all behind me, but it's still really hard.
I can't advise you, but if you live in the US, the suicide prevention lifeline is 1-800-273-8255. I've called it, and they are helpful. There are no costs or strings attached, so if you are feeling suicidal please call it. If you are not in the US, I'm sure there is a similar number you can call in your country. Google it.