Or not being a choice at all. First of all: I'm writing on my phone, so the format might be a bit off. 
Long story short, i developed feelings for this person. I've never, in my 20+ years of being alive, had such strong feelings for anybody. They know how to make me laugh, how to comfort me. They're very easy to fall for. Even typing this out makes me feel ashamed. 
For a while I thought they could return my feelings. We spent a lot of time together, talked a lot. They know a lot of things I would never feel comfortable sharing with anyone else. But lately I've noticed that they most likely have feelings for my best friend, and i think she feels the same about them. It broke me. Of course, i would never try and ruin things between them. They both mean the world to me. I help them become close, even though it hurts me so much. I've never felt so alone and unlovable. Sometimes I think my crush got close to me, just to be closer to my friend. 
I've struggled with depression for years, but this made my world crumble completely. I realize that depending on a person for your happiness is very unhealthy, but i can't help but feel very empty without them. Knowing that I was just used breaks my heart. I wish I wasn't so naive. 
Seeing them happy hurts. I can't show it, but watching them become something breaks my heart. I was never an option. Not even a friend. Just a tool. That's what I've always been. 
Coping with feelings is hurt. I cry a lot, do a lot of dumb stuff, like getting drunk, doing anything just to feel something other than heartbreak. Haven't been this bad in years, the realization that people don't take me seriously triggered my suicidal thoughts. I don't know how to deal with these feelings anymore.
I am ashamed to admit that i am obsessing over someone like this. Being apart feels like my world is about to collapse. Losing someone never felt this intense. I can't sleep, i can't eat, i can't focus on life. All i could think about is how naive and stupid i am. 

Sorry if this is the wrong place to vent about sth like this. Been struggling to keep it to myself for the longest time.