Whenever I answer any question about suicide, I pray especially hard that God will give me the right words to say. I know that someone might be reading this who is thinking about that terrible, final act—and I never want to say anything that might encourage them to do it. God wants to help them, and no action brings greater pain to those who are left behind.
Nevertheless, I regret that your friend upset you by saying suicide is the unforgivable sin, because this is not what the Bible says. Only one sin can never be forgiven by God, and that is the sin of turning one's back on God and rejecting His offer of salvation in Christ. If we reject God, then God has no choice but to reject us. In some cases, rejecting God may lead eventually to suicide (as in the case of Judas), but not always.
God alone knows our hearts, and while suicide is never His will, He knows the pressures and difficulties your husband faced. Remember, it is by God's grace we are saved, not because we are perfect. The Bible says, "For it is by grace you have been saved, through faith" (Ephesians 2:8).
Take comfort in Jesus' words: "He who believes in me will live, even though he dies" (John 11:25). Then ask Him to help you reach out to others who grieve or may be hurting, and to point them to Jesus, who alone gives us hope.