Aw, he offered to bump knuckles--and you want a birthday card, TOO? I'm kidding about the knuckle-bumping, but really, you are getting divorced. I don't think most people in that situation send cards to each other--some do (my first husband and I did), but I think we are WAY in the minority.
You can be grateful that he isn't fighting, and is being fair through the process. I know, it's how he should behave anyway, but plenty of people don't--and they aren't all alcoholics, either. That's what the mediator meant--I'm sure he or she is appreciating not having to deal with the acrimony for a change. And it doesn't really matter how much he is drinking or smoking right now. Whether he is telling you the truth or not doesn't have to affect you.
I'm glad you had a nice birthday. You will have lots and lots more. Life will keep getting better. Just keep breathing and keep putting one foot in front of the other.
Hugs,