I look at my own family and it's not always smooth sailing between siblings. With all the added pressure they have, it's magnified.
I don't blame what's his face and the actress for wanting out of that situation too. They aren't in line for the throne. Given this, what's the pay off for all that abuse and scrutiny? She also has a lot of money and he probably does too. So they can go live a nice much quieter life together and enjoy themselves without that circus.
Money is nice, but fame seems horrible, especially with the British press. I don't think that actress fully realized what she was signing up for.