I'd be more upset at a friend for cheating on their wife, than hooking up with my ex. I'll never understand how people feel they have some weird ownership over their ex(es). Your ex is your ex for a reason. Your friend is a dirtbag for cheating on his wife, but not hooking up with your ex.
I personally thin that he should have had enough respect to not chase that tail at my house. I have no illusions of having control over my ex, but she isn't going to be allowed to get laid at my house. Wanna do it somewhere else? Go for it. I'll still be disappointed in him and would just as soon see him get in trouble with his wife and lose the house, truck, and kids. She is a cop too and she DEFINITELY won't be happy. She will discover it on her own since I know that she reviews their phone bill since he has been caught cheating before. I guess he can just kiss my ass and lose his house, truck, kids, and job for conduct unbecoming an officer. I know his chief personally and he tends to hang with Chrisrian values and get rid of those that don't.
I wouldn't worry about how his son is being raised, you've got enough on your plate already. You can't change people, but you can modify your thinking and be a better role model. Having a physical altercation, or even raising your voice, is definitely not the way to do this. It's too late for the adults, your friend (now ex-friend) and ex-wife, but if you take this approach, in the long term you'll be much better off, your current marriage will be happier, and so will your son and his friend.
What he did was very disrespectful according to the male code. However, she is your ex so your gonna have to let her do her 'thing.' The guy obviously has some issues. I have anger issues when it comes to certain topics and this is def one of them. I suggest keeping him at a fair distance just so as not to ruin your son's friendship. Other than that fuck him, hes a cheater and obviously has low morals/standards. Let karma deal with him and DONT stress/overthink about it. This is the best cure from what ive found. Focus on your harvest. Also why the fuck would your female acquaintances say you have feelings for your ex considering the situation?? That is utterly ridiculous.
I think you should just let it go, man the only reason it would bother you is if you still had feelings, and if youre happy with who you're with now, than fuck it, It's not like you can change their mind about how they feel about each other So I think if you try to take action you'll only lose a friend out of it, you know?
I wanted to add one more thing. The fact that he knowingly made the choice to engage with your ex despite knowing the relationship your sons have with one another is pretty disrespectful. He's a married man and should be devoting his time to better his children and wife not sleeping around using his 'cop status' to get pussy.