I find mine is the same sometimes he is very nice and has done me favours with the kids, but other times he is the biggest arse ever.
My catch phrase just now seems to be "Its always something".
I find the best way is not too expect too much, and not to beat myself up when it is him that lets the kids down, I get so upset when he doesn't want the kids for as long as I think he might or whatever. But the kids don't seem bothered I suppose that is just as sad as if they were upset.
I have to just remind myself that I am good enough to be bothe parents and that my children ar wonderful and love me. ExH is just a very small part of that.
Now that things are starting to get signed off with the solicitor I ma starting to get a bit more tough, but determined not to play tit for tat using the kids even though he might try.
I have learned after a year..
keep exH at arms length,
don't be fooled by his good days,
don't get too chatty, it never lasts,
make sure all arrangements are very very very clear, written down if need be,
don't leave things open ended sort out times for pick ups etc beforehand so no confusuion.
do not be rushed into agreeing to things you are not happy about, take time to think and discuss if possible,
it requires two of you to negotiate,
don't be arsey, bitchy etc it gets you nowhere,
be the grown up!!!
hope things settle down and you get things to a reasonable state.