I feel completely worthless

I was teased a lot for my weight in middle school, ive since lost the weight and think im at a pretty healthy level in that respect but I think that teasing has instilled a submissive tendency in my mind and ever since I dont really think of myself in situations and let people walk all over me. I started having feelings for this friend of mine and for the past year I've gotten pretty close to her and have spent a lot of time going out of my way to help her with things and would still do anything for her. Ive known that she doesnt feel the same way about me but have acted the same way towards her, today I told her that even though i have feelings for her our friendship is much more important and that all the things i do for her im doing as a friend and not going for anything more. She pretty much brushed me off in the most convenient way possible (for her) after I told her. I feel like something has to be wrong with me and that i must be worthless if i can be discarded so easily. People always tell me im a great guy but i feel like im just a nice guy in everyones life and that if i wasnt there no one would really notice or care. Ive thought about suicide a lot but have been persuaded the other way by two of the only people that i think actually care about me. I just dont know what to think or do and cant help but feeling completely worthless.