He is who he is, Kelly. Right or wrong, better or worse. And rather than waste any time or energy "hoping" that he won't spend your tax refund stupidly, b/c it's a fair bet he will do just that (right? Past behavior is a good predictor of future behavior...), is there any way you can squirrel at least part of it away before he gets to it? Start making that escape plan for you and the kids.
Someone here once said "Hope is great, but it's not a plan."