I hate to be the word of reason... but in life you reap what you sow. It's only fair for your husband (ex?) to have a chance at a meaningful relationship... just as much as you do. Your infidelity destroyed the trust in which any relationship depends on and it is his right to want to continue or end a relationship (just as you have the same right). Apparently he has chosen to move on... and all you can do is the same.
My condolences on the consequences of your actions... but hope you will not pass along your feelings to your new child. If nothing else, you have an opportunity to make things right for this child... to be the best mother you can be.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen