Welcome back, Guinevere.
With my son, the early signs were evasiveness and attitude. He'd not want to say where he was going, stating that he was "a grown man and didn't have to be accountable". Gee, I am 105 years old and I still tell people where I am going, lol.
I could spot a relapse a mile away and there was no point even discussing it with him nicely, his ears and mind were already closed.
Of course money and VCR's missing were a giveaway too.
Hugs