What is your advice to a person who has become addicted to gambling, has lost his money and other people's money, and is now contemplating suicide because of debts and problems?

The door of repentance is open. Therefore, you must sincerely repent and immediately abandon the sin, and distance yourself from the causes and people who invite you to it. Lost money is a trivial matter compared to your salvation from evil and attaining Allah's pleasure. As for debts, strive to repay them to the best of your ability, and if you are in hardship, make that clear to your creditors. It is permissible for you to take from zakat (definition) funds if you are repentant. Your thoughts of suicide must be repelled, as it only increases Allah's wrath and punishment, and will not relieve you of anxiety.