"I feel the opposite way about my ex-wife (mother of my kids). If she died, I would be throwing a huge party. I'd celebrate, not cry."
If that were true, then it sounds like the writer of the question has some bigger issues, himself. So many people like to think they'd be one way when they haven't been in a situation before, but they might surprise themselves.
Hell, if one of my exes from 20 years ago died, I'd be sad. I mean I wouldn't be sitting there for weeks depressed but this is someone you shared memories with and being sad is natural. Someone died, someone who was close to you. If you were sitting there throwing a party I'd think you had a little Patrick Bateman in you.
In fact, re-reading this guy's question, I think he is a bit of a dick. "Oh, this guy was in prison, this guy didn't pay child support, he was a piece of shit"...well aren't you Mr. Knight in shining armor, then...coming around to shit talk the kid's dad. I've dated women with kids and I would NEVER discuss their father no matter how bad I'd heard he was (and unless you KNOW the dude, it's still just hearsay), unless the kids brought him up. And even if they did, I'd listen and talk about their feelings about it, but NEVER talk about how I felt about the dude. You don't shit talk a kid's dad to the kid.
Sounds like the dude feels threatened and wants to be the only one in their lives, physically and mentally. Life doesn't work like that.