When I first heard that Kate had HG, my first thought was "uh-oh, how taxing it must be for both of them."
It's debilitating not only physically but also emotionally as well -- with all the press watching everything, it can take a lot of toll. HG can have other negative consequences such as:
3) strain on the relationship between husband and wife (I have heard from other HG women how their pregnancies had a very bad impact on their marriage. Husbands are often required to be both physical, mental, and emotional support for their wives. I know I couldn't do anything without my husband - he made food, washed me, did all the household chores, and took care of our two dogs all on his own while working on his doctorate. This results in stress for both man and wife and if it isn't handled properly, HG can lead to serious resentment or even divorce. I really do hope William will be patient, gentle, and supporting throughout Kate's HG)
I don't think we have to fear for their relationship unless there are severe external factors playing in, which I can't see there are or William is very inconsiderate, which is not my impression either.
However a pregnancy, especially a first time pregnancy is a pretty stressful period for the man too. If for no other reason that you feel helpless. You can't do anything to take away the obvious occasional comfort of your wife and you often don't know what foot to stand on and there are times when, no matter what you do, it just isn't right.
It gets even worse if there are complications or the pregnancy is hard (as would appear in Kate's case) or just when your wife is alarmed, because she's just as inexperienced as you - that can really freak out any husband even though you try to hide it.
You think you are fairly prepared because you've read all the books, talked to friends and listened to the advise from nurses and doctors - you ain't!
And you think, the next time will be easier - it won't, you are just more experienced.
But that is weighed up against the positive experiences, reinforced I guess by something hormonal or biological which the pregnancy triggers. Apart from loving you wife, which you do, your protective and caring instincts go into overdrive and there is also very much a macho feeling of pride. You do get a different status among the other males from becoming a dad.
And if you think pregnant women can act irrationally, dads are up there as well! - Like going out to buy a remotely controlled car for your infant son.
It gets even more irrational if/when you get a daughter. I don't know what biological mechanism sets in, but the thing about "daddy's little girl" is absolutely true!
And then there is the grandparent-factor.
You will as a firsttime parent to be experience with amasement how your otherwise sane parents and parent-in-law go completely ga-ga.
Oh yes, Kate and William are in for some interesting months.