What’s the problem? I’d be fukking furious if I was out on the road making making for my family and my kid’s mother had some dude taking them to school.

And this is reason #83373628 why you don’t date women with kids.
You mixed 2 different things.
a. Obviously they are not together because he would have flipped out when he realized there was another man in the house.
b. He's not making money for "his family "- He's making it to support himself and giving her money for their son(obviously she doesn't have him on child support, which is probably a favorable deal for him).
They both have moved on from the relationship. She has a new relationship, trust the guy around her son and she needs/wants the help of dropping him off at school.
Situation literally happens everyday in the world.