Is Suicide an 'Unforgivable Sin'?

In this episode, Dr. Betters answers the question, "My fiance, a 35 year old veteran, hurt himself after days of no sleep. I found him when I came home from work. It has been 3.5 months since I lost him, and I worry about him constantly. I know what people say about suicide and heaven, and I hate the thought of him suffering. Does suicide really mean he won't go to heaven? I long to see him again, and for him to not be suffering anymore. Please help."