Your therapist should be able to help you explore boundary options based on your specific situation. Based on what you posted above, it didnt sound like you were aware of the relapse which possibly means there were no obvious behavioral changes in him which affected you?
Addiction has symptoms, one of which is sneaking, hiding, denying the problem. My husband did it too. It really had nothing to do with trying to hurt me, and it had nothing to do with his morals or character.
If your husband is still in the hospital? I think you should turn to their resources and speak to his doctor. A medical education on addiction/alcoholism is the best in my opinion. There are many resources for family members including therapist who work primarily in addiction medicine. These people help family members navigate the process.
At one point I was ashamed of what was happening in my family and due to this I isolated from my parents and long time friends. It was a huge mistake on my part because those who knew me best, and cared the most about me and my husband - those were the ones who were able to provide me the most support.
As a side note. For me, the most important boundaries are based on health and safety needs, and the care of my child.