I never thought his motive was to be with the AP exclusively, especially if the AP is married and/or has a family (speculation only - I have zero info on the AP other than what's been mentioned here).
I don't know how it is in CO. I've skipped over a lot of the divorce/support legalese, and I would imagine laws vary from state to state. But in our state, the courts and DCS are extremely biased towards the mother both with physical custody and financial support. It is not unusual for a man to pay out far more than he can realistically afford and get next to no time spent with his children. If you lose your job and get behind it's nearly impossible to get caught up. Eventually get another job and make more, often the mom will apply for a modification then they take more. I've seen and heard a lot of bitterness from men who miss their children desperately and are fighting thousands in back support while trying to avoid license suspension and jail as consequences (that really helps a man work and get caught up, right?).
I am NOT saying this could or would have been CW's motivation as I don't know. But divorce and looking at supporting 3 small children for close to the next 20 years, if you want out, want your total freedom and are detached or psychotic enough to snap like that, it's absolutely a big motive without a specific AP.