Will he regret his affair? Maybe he will and maybe he won't. The best thing you can do is live a full and happy life. People often talk about them getting their dosage of karma, what goes around comes around and all that, that is something you can't control.
The best way for them to get their karma is to see you living a full and happy life, do things you've always wanted to do, learn a new skill, get a hobby, meet new people, laugh and spend time with your son.
In the beginning it hurts like hell, it took me years to realise that I was wasting my time and energy wondering if my ex was happier, full of regrets. I eventually realised they weren't worth my mental energy.
I have realised I am so much happier and better off without my ex. Get support from your friends and family, read books, maybe go to therapy, keep posting in forums for support.
There's a fantastic website and forum for people like you and I who have had our hearts broken called www.chumplady.com
You will get thought this, your ex is an idiot and has come out with the same shit most cheaters speak.
Keep going, stay strong and fight for you and your son.