Lights, this is a delicate situation. In your letter you said that because the Word tells me to forgive him, I forgave him. But what does your heart tell you? Do you really want to forgive him? I can do what the Word tell me to do, but I may do it half heartedly, I'll do it because I 'have' to.
You must begin to trust him again, or your marriage is over. He's fallen into a trap and the last thing that he needs is to fall further. You don't want to act like the Church today, they fold up their arms when someone falls into sin and bar the door so that they don't get in, unless they take a 12 step program they won't forgive him.
By not trusting him, your going to lose him to another woman or he'll go further into drugs, and your going to grow bitter and hateful as the days go by. I know this because my Sister has gone thru this mess. But her case was another woman. One day, they both sat down and he told her about the other woman, why he fell for her and thus and thus. Because they both opened up to one another and displayed their fears and such, their marriage is on the road to recovery.
You need to hound him to get answers. Pray for him yes, but get at him. Don't let that devil take your man. See beyond flesh, see beyond the drugs, see a soul that needs to get things right with you and God. You need to find out why he has gone to drugs again. When he finally opens up, be prepared, you never know what is revealed, so learn to not take offenses. A quick way to get rid of an offense is to boldly inquire at that moment as to why such and such was said, and display your feelings to that person and how you felt about it. Holding something inside without talking about it does more injury to your spiritual walk, and furthermore, God doesn't hear our prayers.
You need to TRUST him again!, Think of the times that you have sinned, did the LORD remove the holy Spirit? No, He has ENTRUSTED you with His faith to see you thru.
Your in for a battle, so mark that down in your mind.
1 Corinthians 13:4 Charity suffereth long, and is kind; charity envieth not; charity vaunteth not itself, is not puffed up, 5 Doth not behave itself unseemly, seeketh not her own, is not easily provoked, thinketh no evil;7 Beareth all things, believeth all things, hopeth all things, endureth all things.
Your going to endure this, and your not going to harden your heart, your going to love that man, your going to pray for him and your going to stay close to him.
God Bless
Com