If they are comfortable talking to you about the condition, and if you are comfortable listening, it could solidify your relationship.
If you are not comfortable with that type of thing, that’s okay also.
I have a friend who used to have it and does not have it anymore.
It can often be controlled by a healthful lifestyle including healthy exercise, sleep, nutrition, and supportive relationships.
Although you do need to be realistic, especially if you consider marrying this person. If you find that your significant other leans too much on you between the high highs and low lows that characterize Bipolar Disorder you may want to suggest that they see their therapist more often.
Many mental health clinicians have the opinion that Bipolar Disorder is over diagnosed when often major life stressors or past events that need to be addressed in therapy play a bigger role than we know in the disease; do not dismiss them for their weaknesses if you are captivated by their strengths.
Another common positive trait among those who suffer from Bipolar Disorder which is depicted in many books is how gifted they are and how strong their imaginations are.
It’s also important not to go into diagnosing your partner with bipolar disorder if they have not told you they have it.
If they are sad one week because they lost their cat and on a high another week because they have gone skydiving, that does not necessarily mean they have bipolar disorder.