been there done it, got the tshirt.... a couple of times.
Honestly I never had problems with earning difference, even when the wealth gap was extremely wide.
It's all about personality and the way to deal with each other during the relationship.
As long as the economically strong half of the couple doesn't "rub it in" too much then everything is fine.
The important is to be equal in our behaviour to each other.
However sometime can be upsetting.
I remember one "funny" event with a rather wealthy woman.
We have been known each other for over 10 years and had a very passionate relation even if we didn't meet that frequently (every second month).
Once we went to dinner together at a restaurant.
During the dinner she started telling me about her day and work ... pretty heavy routine of start working at about 7am and finishing at midnight...
However she also said that she made good investment and got 10M US$ out of it over the week-end.
I was happy for her until... she wanted to split the bill!
Damn! she could at least pay for the dinner.