it definitely is the choice of the individual, no one can really stop you. (unless assisted, thats a whole other ball game)
however, the void pain, grief, misunderstanding and sadness to family/friends that you leave behind feeling, that is awful. Also why it is often refered to as the cowards way out
I must say that i have had many terrible times, and contemplaited it. My mum attempted it a few times, due to her illness, if she had succeeded i don't know what I'd have done.
i know, if this question is relating to you, that sometimes it is the easier way out, and sometimes feels like the only way out, however it isn't. life does get better, you become a stronger person for dealing with the issues surrounding why you feel like this. Pls dont do anything rash, give yourself time, try to think of positive things (I know, i know, thats virtually impossible), and talk, even if its to the Samaritans.
good luck, time does change things and does get better, even if it seems that it wont.
x