Adapt the career to the relationship.
Careers aren't always defined in detail. Many careers need a whole lot of detail oriented change to make them work.
The thing to do in a relationship is, make the relationship part of the career. The new career is a combination of the old career and the relationship career. If both partners don't recognize this, it will be more difficult. But it doesn't stop there.
If both partners in the relationship are career oriented, the new careers will need to be made from the relationship plus the other partner's career. For example.
Partner-A has Career-X. Partner-B has Career-Z. Into the relationship...
Partner-A has the new career of:
Partner-B = major;
+ Career-X = intermediate;
+ Career-Z = minor.
Partner-B has the new career of:
Partner-A = major;
+ Career-Z = intermediate;
+ Career-X = minor.
This, again, changes when the kids come along.
If people don't recognize this, and don't work it this way, odds are that something will fail in the relationship.