A friend of mine committed suicide last December, at your age and from what I can tell, in a similar situation (he was even also a previous YC participant). It hurts how much reading this reminds me of him.

You mention some people know this side of you (to what degree?) but that they don't know how to help you. I think it's critical that during this rough patch you're going through, in addition to receiving anonymous advice here on HN, you surround yourself with supportive people in real life. Even if it's just one person that sticks with you through this, that you are completely open to and stay in close touch with about your plans and progress as you try therapy, medication and various other techniques.

For ideas on how to involve other people without having to be embarrassed or being too much of a burden, read about Jane McGonigal's "recovery game": http://blog.avantgame.com/2009/09/super-better-or-how-to-tur...

I wish you all the best.