PhD student and postdoc statistics related to relationships
This study has "postsecondary teachers" divorce rate at around 14%, and "Other education, training, and library workers" at 15.6. 

For reference, "Computer scientists and systems analysts" were at 15.64. 

Both were below "verage US Divorce Percentage" of 16.35.

Most occupations typically associated with financially secure lifestyles (doctors, engineers, CEOs) seem to fall &lt;= 10%. 

Most occupations not typically associated with stability or prosperity fell >= 20%. 

Predictably, it appears that financial stability, on average, brings an order of magnitude increase in the stability of marriage. So all the girls looking to marry a doctor or lawyer (or engineer??) really do seem to be statistically more likely to live happily ever after ;) Likewise for all the boys looking to marry up.

In my relationship, we went through a total of 3 graduate degrees, for 2 of which we were both in school at the same time. 

That definitely helped, as each of us had first-hand experience of living below subsistence level while in grad school. We were able to mitigate the inevitable adverse effect of financial insecurity on a relationship by being understanding and patient with each other; developing judicious spending habits; living below our means; and understanding that, in the long run, a relationship of the kind that we have is more important than a job, a salary, or a lifestyle.