The outcome will be what it will be; you have no control over that.
However, the higher concern is that after three years you picked up. That's what I would be focusing on because that is the true problem; not what your boss thinks about it.
To keep things in perspective, it sounds like he gave you a warning; you've given yourself a warning, and you have to redouble your efforts; return to AA and work your program and treatment, and things will go the way they are meant to go.
One foot in front of the other. I have often heard that all that misery can return whenever we want it...all we have to do is pick up that first drink. I think you learned that first hand.
There's nothing you can do to change the relapse, but there is plenty you can do to ensure it doesn't happen again.
IMO it has more to do with what you do going forward, then a momentary lapse in reason. Walk the walk.
We'll all help you with the walk. Keep your chin up and move forward.