You just finish describing my relationship with my partner. We meet as teens, we fall in love and dated, and he broke up with me. We stayed friends, best friends actually. Each one dated other people and sometimes, something could happen. He falls in love with a girl. Seriously in love and I couldn't stand it. Needed to move on, so for 4 years, we didn't speak.
Once I started seeing again other people having other relationships, we started to talk again, only as friends. I eventually meet the guy I would marry... and then divorce. Meet even someone else... and it made some years I was not talking to by a best friend, he sent me a mail, asking to drink coffee, We didn't even remember why we stop talking. And we started to hang out... each time a bit more. Until the boyfriend, I had at the time broke up with me coz said I was cheating with my best friend (I wasn't just to let that clear).
I send him a text "It's over" he replied he would come to my flat with wine if I cooked... We Drank too much, and we end up sleeping together and it was perfect. In the morning when I woke up I thought he is gonna say it was a mistake and all that jazz is gonna happen again. He stayed. He came back every day.... and 7 years after we are still together. He is still my best friend, but he is also my partner, one of my strongest pillars in life.
I loved him since I am 15... I am 36, the love you feel for someone can change. It can become sexual, platonic, romantic, or just love. But it would be unreal for me to have a friend that I would put before him. And I was married, but he always would come first, so I think my story gives you the answer you seek.