Mind asking something easier?
Oh well, it's a kind of a problem not so easy (if at all) to solve. There are several answers popping up to mind:
1. He was unhappy and could not bear the life any longer (simple, isn't it?)
2. He was cursed by Morgoth (through his father, Hurin)
3. He was under the influence of Glaurung's spell
4. He killed himself as a weregild for the death of his kin and friends the cause of which he himself was
I deem the 'real' cause was the mixt of all those together
Personally for me, he was horribly wrong comitting suicide at all.
Hum, as an aside, I'm now Ghost-Prince! Yuppie!