What a piece of work he is.
Sometimes it's better to frame things in a different way.....
maybe he was never the person you thought he was, maybe he actually never really loved you, maybe you never knew the real him and how he really felt about you. Maybe you didn't loose love, but never even had it with him in the first place. It was all just a deceptive illusion.
The tough patch of bringing a baby into your marriage, just made him bring out his true and honest colours. That he's a cheating scumbag.
While you're hurting now, ultimately time is a great healer of wounds. Allow yourself time to grieve and get over the trauma. It's ok, to not feel ok sometimes. That length of time varies, so don't chastise yourself if you think you're taking too long to 'get over it'. You'll heal in your own time. Get a good counsellor if you can and talk about it.
Learn to look at the new direction, opportunities, and freedoms you'll have now, that you didn't before when with him.
You might now do less domestic duties (no more washing his laundry) less childcare (when he takes DD on weekends), parent your way (discipline, outings choice etc) and live your way (pursue the career/hobbies/socialising) you've always wanted without having to negotiate every thing in life with him.
Better to live in bitter truth, than in a sweet lie. At least you're not fooled by him anymore.