Sure enough it's a sin to kill someone but to kill yourself is that evil after all as a Christian you need Faith in Jesus to go heaven and what of Samson who killed himself with the Philistines I just want to know if the Bible says suicide is a sin?
Not planning suicide, but incase I need a backup plan

yea...

According to Bill Maher Suicide is man’s way of telling God, ‘You can’t fire me – I quit.'”
it doesn’t take away the pain, it gives it to someone else.
If you’re going through hell, keep going
There was no godly man who committed suicide in Scripture. Of course this doesn’t mean that a godly person can’t, but we should take this into consideration. The case of Samson wasn't suicide per say because if he had the choice to live he would have .
Suicide itself is murder because you are taking life that you can't create. Many people will say it’s self-hate, but it is probably the strongest expression of selfishness and self love. Many people kill themselves because they want something that they don’t have or maybe they lost something and thinking only about themselves they take matters into their own hands and kill themselves.( James 4:2, Matthew 5:21). Is it normal that you would wake one morning and kill yourself? No. On a normal day can you pierce yourself with knife? Wouldn't you be scared a bit? ( Eph 5:29,). Now ask yourself this question, would suicide resolve the problem am facing?
One of the questions we have to ask ourselves is suicide really enduring to the end? Certainly not . as far as you are human, you would face trials and temptations. The bible admonishes us to endure ( Matthew 24:13).
If you have a burden, cry to the lord Jesus for help ( Matthew 11:28, Psalm 43:5, psalm 34:18).
God’s people are known as people who persevere and have hope. They are not quitters. When you commit suicide it is saying I have no hope, I have no future, I have no purpose.( ROM 5:2-5, 2 cor 1:10). Don't give up because God hasn't give up on you.