I am so sorry you are going through this and hurting so much. Please understand the drugs are fueling your husband and his feelings. On OXY they just don't care about anyone or anything, just their drug.
You are grieving something you lost, something you believed you had. It will take time but as Kindeyes said, you will have a brighter future. Believe that and know it. You will no longer have to watch over a drug addict and try to keep track of his lies. You are not a failure. Your husband decided to do drugs. You have no responsibility in that. Now you are taking your daughter out of a chaotic and stressful household and taking good care of her. That takes strength and guts. Don't be so hard on yourself! Hugs.