I'm not expert on this, but patience is the key and backing off. If you are there when he picks them up today? Then be upbeat and pleasant, act like you have plans. When you're acting desparate and needy they know it and don't like it. He's going to do what he wants to do, the only person you can control is yourself.
I used to cry and be sad when H would come to visit son, but eventually I got sick of acting so wimpy, so was determined to show him I could be happy without him. And that it wasn't all about H!
The way he keeps changing his mind he really doesn't know what he's doing.
