The best response to that question, is found in the Catechism of the Catholic Church:
Everyone is responsible for his life before God who has given it to him. It is God who remains the sovereign Master of life. We are obliged to accept life gratefully and preserve it for his honor and the salvation of our souls. We are stewards, not owners, of the life God has entrusted to us. It is not ours to dispose of.
Suicide contradicts the natural inclination of the human being to preserve and perpetuate his life. It is gravely contrary to the just love of self. It likewise offends love of neighbor because it unjustly breaks the ties of solidarity with family, nation, and other human societies to which we continue to have obligations. Suicide is contrary to love for the living God.
If suicide is committed with the intention of setting an example, especially to the young, it also takes on the gravity of scandal. Voluntary co-operation in suicide is contrary to the moral law.
“We are stewards, not owners, of the life God has entrusted to us. It is not ours to dispose of.”
As we are told in 1 Corinthians “You are not your own, for you were bought with a price.”