responding to sarcasm

My ADHD husband and I are at the point of separation after 30 years of marriage.  I just told him that I plan to move out in September.  I did a lot of work on my own to get to the point where I clearly communicate my boundaries to him, and he is using one of his most common conversational weapons to respond to me...plenty of sarcasm. The problem is that I truly can't tell any more if he is being sincere ("Sounds like a fair proposition") or sarcastic. I am wondering if anyone else has any suggestions for overcoming this. (I have been asking him to please avoid sarcasm for a long time)  He acts insulted when I ask him for clarification because I am not sure what he really means.