Snide (IMO) comments;
"so your husband had an affair, and the woman got pregnant, and then you went and had a baby with him AFTER that?
"
No idea why that poster was confused. The OP was clear that that was indeed the situation.
"Does it not bother you that your Dh hasn't ever seen his child?"
Nothing to do with the OPs question.
"Your (d)h's other child will definitely be hurt."
Why 'D' in brackets? The OP says they're happy and surely it's the default to assume married people are happy and would refer to their spouse as 'D'whatever.
"If you do insist on staying with him then tell your dd the truth."
Why us the word 'insist'?
"Lying to children is never good. Though I suspect you will keep it a secret from her to protect your dh
"
Just a horrible dig at the OP.
None of these have anything to do with the question the OP asked and are just bully-boy, snide comments.
You said that the OP hasn't covered herself in glory for 2 reasons; forgiving her husband and supporting his having nothing to do with the other child.
I don't like the sound of the DH not seeing his other daughter but it may have been at the other woman's request or wishes. She may have been married too. I can think of several scenarios where him leaving the picture could be for the best for all involved. He pays for the child which is in his favour. Anyway, the OP didn't ask for judgement, she asked for advice. Why she responded in kind to the comments she received she was patronisingly told to "cut the attitude".
As I said, a quintessential MN thread.