The question isn't "why is he so nice now?" - - it is "How long would his "niceness" last if I let him come back?"
Often alcoholics have a cycle they go through: the honeymoon, the plateau, the disillusionment, the "blame anybody but myself", the anger, the hostility, the bad behavior...
And that leads to them being tossed out, and they want back in, so they try THE HONEYMOON again... and on and on it goes.
You don't have to buy back into anything you don't want to.
ShootingStar1