Nothing about suicide is painless. Ask anyone who has contemplated it; tried to accomplish it; known someone who did it; tried to understand it.
Most people who are considering suicide are in pain. It may not be the kind of pain that others feel, but it is there and it is overwhelmingly real to those people. Suicide then becomes an option to relieve pain. That being said, it is also a choice. Ambivalence lives in the suicidal person; often the balance is tipped towards a final action. At this time no other options exist in the mind of the person in pain.
Do not blame yourself for not interceding at the crucial moment. It is often not possible. The suicidal person may be experiencing this only in private - in thoughts alone.
Often the connections made before the event that can - but do not always - prevent the decision to turn thought into action. For those of you who can relate to this, here is something that could be helpful. http://www.metanoia.org/suicide/