If the kid is male, he becomes a non-mahram after puberty. So even though this woman raised him, she cannot be around him alone. Unless she adopts him as a baby and suckles him.
Likewise, if the kid is a female, she cannot be around the 'father' alone after reaching puberty and has to wear her hijab and qulnus all the time.
And to answer you first question, you won't know the emotional pain of not being able to produce a child unless you or your wife are incapable. Desperation can lead someone to anything, unfortunately.