Let's turn that around- what if you give H 50-50 custody and he turns into Super Dad? What if he's involved in their lives like he's never been before? You said it right here:
"My H has made A LOT of changes regarding his parenting of our kids. I have told him on several occasions that I am really proud of him. My H spends a lot more quality time with the kids."
I think your fears are based on who he was rather than who he is. Next time he throws out 50-50 custody you might try responding with "you know what? As much as I don't like the idea of not seeing the kids all the time, you have been a greatly improved father lately and I would consider a 50-50 arrangement." His response will tell you whether he's saying it as a "threat" or whether he really does want them more often.
