I just want to send you a virtual hug. I can relate to a lot of what you're saying, long distance, never ever ever imagining that he would cheat, and the comparisons.
My WH cheated with a thinner 20year old ( I am 27, he is 25)...and I had never ever had an issue or felt self conscious about age before, but I immediately started comparisons. And that is not a kind road to go down. There is nothing happy that you will find on that road if you start going down it.
One thing I have learned from talking with friends who have gone through similar situations, and from reading a whole bunch of info on this site is this; it has nothing to do with you. It has nothing to do with how much better at '________' the OW was than you, it has nothing to do with you being you and her being her. It has to do with something that is broken inside of him, which he needs to fix, and likely needs your support to fix ( if he is willing to fix his 'brokenness" that is), and if you are willing/able to support his growth.
Please do not go down that road of comparison...I have lived there for 4 months and it has taken an incredible toll on my self-esteem and it is completely false.
I can relate in part to your story, though I have never been pregnant and as far as I know I don't have fertility issues, but we went through a lot together too ( on a different level, surely). I remember reading a psychology article when I was in University that told about people who go through traumatic events together ( plane crashes, earthquakes, etc) being somehow more strongly bonded than they would have been had they met under different circumstances, or had they never experienced such trauma. I assumed that when our puppy died, mere weeks after I was dragged down a street by my throat, behind a car, in a robbery, where I nearly died, and he helped me back to health...I assumed that after we got through these traumas, that we would be stronger. That our relationship would be somehow strengthened and would be better. For a while it was, but then, the A happened.
I don't have advice, as I am still dealing with day to day stuff in our R, but I just want you to know that I hear you, and I sincerely feel for you.
And congratulations on the birth of your healthy little girl, I am sure she is just an angel. Hopefully your WH will see what he is potentially walking away from if he doesn't seek help and sincerely R with you.
I am not sure where you are at in this ( wanting to work it out, or wanting to leave). I just hope you know that you have much support here and that I am wishing everything turns out for you.
Wishing you all the best of everything.