He probably uses every six hours, Elle. That's the way it is with heroin. Two days is too long. Every six hours. This means he is drug-seeking or drug-using all day and all night, and his world is heroin. That's all he wants.
He is delusional about March 31st.
And yes, he is making you crazy.
Are you getting help for yourself? Meetings? Counseling?
His mother has locked her brain. She is a perfect enabler and he will be very comfortable there with her for a long time. Before too long they will both be completely insane.
If I were in your situation, I would separate for an entire year. Most codependents cannot do that. They are too hooked on the addict.
But that's what I advise anyway, when things are bad.
You'll need some help for yourself beyond this forum. Is Nar-Anon in your area?
While you are reading this, he is either on dope or getting ready to be on dope.
You have a hard road ahead, being married to a heroin addict. Please get some help for yourself, you need it and deserve it.
And your son needs a mother who is present emotionally.
NA meetings for your husband are free, whenever he's ready.