Both of my parents are nurses, and they are now divorced after 25 years of marriage...were both nurses at time of divorce...neither has remarried. I don't think nursing contributed though...lots of other issues.
I see a lot of nurses in relationships where they take care of the other person. I think the caretaker role is something we're born with, which is why we become nurses...and if it carries over to relationships, it can be unhealthy.
I think the job itself can also be unhealthy to a marriage, depending on how it's handled by the two people involved.
High stress, a lot of hours, weekends, holidays, night shifts, etc, all take their toll.
Nursing is a career, in my opinion, where we need our S.O.'s/spouses to understand what happens and what we go through to a certain extent, and to be there emotionally for us.
And that can be hard to find.