I am so sorry that you are going through all of this. I completely understand where you are coming from with the questions. It just doesn’t make sense… but from my research into addiction and anecdotally I’ll give you my understanding of it.
If our addicted loved ones told us what was going on, they would be faced with a choice: stop or lose us. They love us, so they don’t want to lose us. But they NEED to use. So lying is the way to do both.
Through my own therapy, I’m trying radical acceptance. To an outsider, nothing an addict does will make sense. It probably won’t make sense to them. But to save yourself anguish, try and work from a place that whatever they did was because they had to, that’s always what was going to happen. They didn’t choose it, and neither did you.
Only you can choose what happens next and what you are willing to put up with.
I hope you find some peace, it’s hard but I wish it for all of us on this forum