Would like to know if anyone has come through the other side for the better?
Yes! I did. I had someone leave me for someone else and initially, it's the pits. I spent a lot of time around loving friends and family, sought therapy (which I was already in) and mentally took myself back to the drawing board to figure out what makes me 'me' and took up new hobbies. This doesn't all happen at once, mind, but little steps and all that. Not even a year down the line but I bounced back as will you.
As for my ex? I suspect he's still with the ow. I recently saw a photo of them together - posing awkwardly, her arms folded, about half a foot between them and he has a terrible attempt at a beard [/schadenfreude]
The point is, even though you feel rejection at this stage, often we choose people who reflect certain things about ourselves. Your ex has gone for this ow based on who he is - a liar, a cheat, emotionally unavailable etc.
Keep looking after yourself, focus on you and your lovely baby and you'll find yourself less focused on what he's up to.