I think there are things both parties can do to weather BP.

Both parties should be in therapy if possible. Even better if they can have couples therapy too.

No matter what mood you are in make the other person feel love. We do this through romance cards, other little things like breakfast in bed, drawing a bubble baths, or little notes. If one of us says “I love you.” but the other is really irritable they'll say “I know that I love you too.” If we realize the other is in a bad space it's “Remember I love you AND need you.”

No arguing when irrational. The person not in the middle of an episode has to let the other have a one-sided argument no matter what that person says.

Absolutely no decision making is “allowed” in the mist of an episode. If the person wants a divorce say “okay” but leave it at that. Do not sign papers.

Always apologizes for wrong doing and forgive! Take everything with a grain of salt because the person in mist episode doesn't mean their behavior or thoughts, no matter how much they insist they do.

There's more but I can't think of them right now.