Doing long distance with a man with Bipolar disorder?

Lauren • 21🇨🇦Christian ✝ and dating the man of my dreams since January, 15, 2017

I'm am currently doing long distance with my boyfriend of just less of a year. He suffers from bipolar disorder (officially diagnosed). I was wondering if there is any advice on how to handle/approach his "low" as we call them (depressive stage) while not being there in person?