Supposedly the guy was in shambles. He still loved her and up until she told him she was cheating, he had no clue and thought his life was full blown Pleasantville. The shock of going from bliss to hell in a matter of minutes, plus a cherry on top of his wife trying to manipulate his kids and the cops/courts not giving a shit, was too much for him to handle I guess. The last my dad heard from him was a few days before he killed himself and all he said is that there was no end-game he could visualize that would be positive. He wasn't going to get the kids, and within a few months his ex would be fully within her rights to have the new boyfriend play daddy to his kids. I just don't think he could live with that reality.
Murder makes sense from an emotional standpoint, which I'm sure anybody in that position would be, however if you allow one iota of logic/reality in, you'd realize that all that will do is land you in prison for the rest of your life, never to see your kids, and your wife will just find another dude 3 months into your life sentence..