Matthew 18:6 But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.
Jesus is not advocating suicide in this passage. He is painting a dramatic picture of the seriousness of damaging the faith of "one of these little ones." Besides, even this vivid comparison describes an execution and not a suicide. Jesus did NOT say "it were better for him that he hang a millstone about his neck..." but rather "it were better for him that a millstone were hanged about his neck..." clearly implying that action would be done by others and not himself.
I hope you have found this helpful.