It's definitely not a long time, OP. Not for something as life-changing as marital betrayal and divorce. My exH left me longer ago than that, and although I certainly don't want him, I'm still pretty bitter about the betrayal. It's a massive, massive adjustment. The entirety of the rest of your life looks completely different from what you thought it was going to be. I think that that's such a truly enormous thing that people who haven't been through it don't really understand. I don't want him, and I have adjusted, and I have had great dates and sex, too.....but there's still the fact that things weren't supposed to be this way, and the fact that every day as long as I live is not what I dreamt and wanted and hoped and assumed it would be. Nor will it be what I was promised. And the fact that he left me with trust issues, and left me trying to find someone else when older and most people had settled down....I think it's the emotional equivalent of having a big scar on your face, I really do, except that scar is on your heart. If he'd only been the man he made out he was, we'd have been so happy.
But he wasn't that man, and neither was your husband. The only thing to do is think about it as little as possible. Keeping busy helps. Significant dates are hard, and it's also hard seeing happy couples around me in the prime of their marriages. Apart from that I don't think about it too much, but I do have my moments. And I can imagine that this news has absolutely thrown you for a loop. But you will feel better - this news is very new.
Marriages that began as affairs have an exceedingly low success rate, so there's that. And he's no prize. He's a man who not only cheats, but does so when he has tiny children and breaks their hearts.
I've been through some tragedies and hard times, and what I've found is that when there's no fixing something, and when you are not in control, like bereavement or divorce issues, the best thing to do is distract yourself, whether with work, films, books, whatever. There's no action you can take to affect what the situation is, like you could if you had a bad job or relationship. So distraction is the key. And the less you think about it, the better. The more you ruminate, the worse you will feel.
You must be fairly young if your kids are that young. Thank God you haven't wasted any more years on him.
Self-care, OP. He's a rat and you're much better than him. And SO much better off without him. This is just a blip.
Hugs xxx
Now go and get busy and try not to think about him!