I am so sorry for your loss. After trying for a year, we got pregnant but the baby died in utero at 4 months. All the women in my office were pregnant, though I was the only one who had wanted to be pregnant.
My SIL was pregnant at the same time and I can't say that I called to congratulate them in the first few days after she gave birth. It was the first baby in our family, but I didn't have my baby any more and it was a hard call to make.
BUT I can't imagine making anyone else feel like their pregnancy was a burden to my emotional state. I think you should have just hidden her posts and not had to see it. Writing her the big letter was over the line. I understand why you would have felt it necessary and how you could have seen it as a way of communicating and building understanding and friendship. I can't understand how she could be expected to see it that way. This is one of those instances where you should have ran it by a friend before hitting "send" and that friend would have stopped you. I don't blame you, but I do think you were in the wrong to expect her to understand the existance of her child is difficult for you to accept.
I am sorry. I don't mean to sound harsh or belittle your feelings. I know how hard it is. But two things seem fair to me: 1. You should apologize. 2. Don't expect things to ever be the same again. He has a wife now and this aside, very few women would be comfortable with your friendship. Pregnant women are fiercely protective of their husbands.
All the best.
Updated
I am so sorry for your loss. After trying for a year, we got pregnant but the baby died in utero at 4 months. All the women in my office were pregnant, though I was the only one who had wanted to be pregnant.
My SIL was pregnant at the same time and I can't say that I called to congratulate them in the first few days after she gave birth. It was the first baby in our family, but I didn't have my baby any more and it was a hard call to make.
BUT I can't imagine making anyone else feel like their pregnancy was a burden to my emotional state. I think you should have just hidden her posts and not had to see it. Writing her the big letter was over the line. I understand why you would have felt it necessary and how you could have seen it as a way of communicating and building understanding and friendship. I can't understand how she could be expected to see it that way. This is one of those instances where you should have ran it by a friend before hitting "send" and that friend would have stopped you. I don't blame you, but I do think you were in the wrong to expect her to understand the existance of her child is difficult for you to accept.
I am sorry. I don't mean to sound harsh or belittle your feelings. I know how hard it is. But two things seem fair to me: 1. You should apologize. 2. Don't expect things to ever be the same again. He has a wife now and this aside, very few women would be comfortable with your friendship. Pregnant women are fiercely protective of their husbands.
All the best.