If I was your DH, and was addicted to nicotine and vaped over actually smoking - I would hide it from you as well. To an ex-smoker it's a welcome alternative.
I struggled to quit actual smoking when my DH was using standover tactics like you are, I felt he was telling me what to do, making it all about him , and being incredibly controlling and it made it so much harder if I lapsed. I couldn't share how I was struggling , so I hid any backsliding. It wasn't a giant "betrayal", it was weakness and fear of his disproportionate reactions.
Consider the level of drama you are bringing to the situation. "Very betrayed" " Crying all night?" " I confronted him again and again.".etc.
You cannot make someone quit an addiction by flinging yourself around all over the place and insisting he stop. Of course he promised to stop, he probably would have said anything to calm you down.
You seem to not be able to address this rationally, or talk properly to him about without making it about you and your feelings. He has no way of talking to you about this calmly, so of course he'd hide it.
I don't see the circumstances you describe as being a giant betrayal, I see it as a man badgered into hiding an addiction he can't stop.
You have more chance of him stopping if you don't make such a huge issue about it. The illicit nature of having to sneak around is just as attractive as the actual vaping.
I think in the scenario you described, promises made under duress don't count.