What A Waste Of Life

I'm in a long-distance, long- term relationship. Recently i've begun to suffer periods of manic, very severe depression but i can't tell my girlfriend because when i do, she doesn't seem to care anymore and if i don't, it takes a massive toll on our relationship. Most of the time, i want to just be alone and she won't let me. Deep down i know i love her but we just don't see eachother enough and when we are together i just want to get away for fear of her realising that she doesn't want to be with me. At nights, and almost every time i close my eyes, i think about killing myself, how, i wouldn't have to deal with anything and i wouldn't feel or think anymore. I know the old clichés about depressed musicians but i honestly don't know how much more of this i can take. I feel like i need to cry all the time but i just can't produce any tears and people think i'm happy because i never seem necessarily unhappy. Please, please, someone, if anyone has any advice please help me. I just want to feel normal and feel like i'm not loosing my mind. please. signed, onevery scared 17 year old.