The National Suicide Prevention Lifeline (1-800-273-TALK ) is a United States-based suicide prevention network of 161 crisis centers that provides a 24/7, toll-free hotline available to anyone in suicidal crisis or emotional distress. After... wikipedia.org Please encourage your father to contact them, or do so yourself. Stay with him until the crisis appears to have passed and help is on the way. Remove any possible means of suicide that you can think of, e.g., guns, ammunition, rope, etc. But do understand that if someone is determined to end their life, you won't be able to stop them and it won't be your fault.
Tell him you love him and that it would destroy you , if he chose to end his life. Good luck and good wishes,