There is no doubt that individuals diagnosed with bipolar disorder can often be difficult to interact with.
Their episodes, their attitude, their way of being can often drive a loved one to a point of wanting distance.
Aside from significant others, relationships where more than one person has bipolar disorder may occur a lot within families as the illness has such a strong genetic component.
If you have the disorder, chances are high that you will have a sibling, parent, grandparent, uncle, cousin etc who does too.
My current marriage is the most stabilizing thing in my life and has helped me manage my bipolar so that I have not had a serious episode since 2005. Despite the above, there is no empirical research that shows a CAUSAL relationship between bipolar disorder and marital status.
We still know relatively little about marital bipolar relationships.
Obviously if both parties have bipolar disorder, the potential difficulties multiply exponentially.