Commiting suicide is definitely a mortal sin, and it leads you to hell or eternal damnation.
Revelation 21:8 states,
"But the fearful, and unbelieving, and abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death."
Killing oneself is an act of murder. It is only God has the right to take one's life.
Deutoronomy 32:39 says,
"See now that I, even I, am he, and there is no god with me: I kill, and I make alive; I wound, and I heal: neither is there any that can deliver out of my hand."
Revelation 21:8 states,
"But the fearful, and unbelieving, and abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death."
Killing oneself is an act of murder. It is only God has the right to take one's life.
Deutoronomy 32:39 says,
"See now that I, even I, am he, and there is no god with me: I kill, and I make alive; I wound, and I heal: neither is there any that can deliver out of my hand."