A, You did the right thing by allowing him to sleep on the couch. At least you knew where he was and could ensure that he got up and out the door w/o disappointing your daughter. Your children need to come first and you have to do what you must to ensure that they are okay and happy.
As for the drinking, poor sap, trying to alleviate his pain that way. Depression and withdrawal go hand-in-hand. They disappear for a while and when it lifts just a little bit, they come back around again, and so forth. It's tiresome when they do this, but it's the way depression works for some.
I do hope that they enjoy their day at the waterpark. They are so much fun, but it takes a lot of energy to stay at it while there. I hope he doesn't disappoint her. As for you and your son, enjoy the day! That's what relaxing is all about.
Keep moving forward!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.