Glam, I hear what you are saying and here's my take on the matter.
1. Were you planning to have a simple lunch at 2 in the afternoon? If you weren't, I wouldn't have fixed a lunch for him. You are not his mother...he should have picked something up and ate it prior to coming over. Now, if you were planning to fix a lunch at that time of the day, then fine, but otherwise...no more doing that for him. Time for him to grow up and learn to fend for himself.
2. Taxes weren't done on Sunday? Well...he better be there on Tuesday to do them, for you only have one day left to file them. I wouldn't remind him...see if he shows up.
3. Listen to what he says he's going to do and then toss it aside. He's babbling and paddling no where fast.
Glam, I wouldn't wait on him for anything. If you and your children have plans and he doesn't show up by the agreed upon time, go on w/o him. He will eventually get the message and may start stepping up to the plate and being on time. By waiting around for him, you are actually enabling him to continue this poor behavior, depression or not. Glam, start living your life as if he's not there. If he truly wants to be a part of it, he'll try harder to do the right things. He's been in the same rut for a long time and something has to shake him up just a little bit to get him paddling down the stream again.
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.