Is suicide justifiable?

Suicide is not justifiable.

However forlorn your condition may be, remember that your experiences in earth-life cannot easily be obtained in spirit-life. 

If you sever the thread of life, you take advantage of Nature's intentions, and cut short your mission on earth. 

Pain sometimes teaches a lesson equally as important as that imparted by pleasure. 

The earth-plane is the rudimentary stage of existence, and primary lessons must be learned here.