"Initially, you can help to make sure the bipolar partner is taking their medication as prescribed," Edelson says. "Later, it will obviously be the responsibility of the bipolar person, but taking medication can be scary, and support and companionship to get going may be helpful."
Rapini adds that often the medications for bipolar disorder can bring happiness levels down to keep emotions on a more even keel, which may make your partner want to stop taking his prescription. "It's the partner's job to be invested. Bipolar disorder is a disease. You cannot talk yourself out of it. Tell your partner, 'If you had diabetes or cancer, I wouldn't let you stop taking your meds.'"
More from YourTango: The Best Gift You Could Give Your Family This Holiday? Nothing.
4. Improve your communication. Use the disorder as a way to connect and open up lines of communication. Let your partner know you're more than willing to talk through problems with him or her. 5 Great Tips For Improving Communication
"It's an opportunity to become closer to your partner," Rapini says. "I'm often so impressed by these couples. They talk more, understand each other's cues better. The more they're communicating, if they are a team, they'll be able to confide in each other."
Dr. Orbuch also says to remember that compliments never hurt. Your partner will appreciate it if you acknowledge a progression in their ability to cope with tough situations. "Be a good listener. Encourage your partner to talk to you and focus on the positives. Notice and compliment what they're doing well and the changes they're making, rather than what they're doing wrong."
5. Take care of yourself, too. Sometimes when you're dealing with the stress of another person's problems, you can forget to take time out for yourself to just refuel. But the experts stressed R&R is an absolute must, along with maintaining friendships and talking to a therapist, if needed.
"Bipolar disorder does not go away," Rapini says. "It's a lifelong illness. The partners [without the disorder] should make sure they take care of themselves. The disease will encompass both people, so keep friends and family close for support."
Edelson also suggested talking to a therapist if you're having difficulty dealing with your partner's condition—which she says is perfectly OK and nothing to be ashamed of. "Living with a bipolar person can be very, very difficult," Edelson says. "It is perfectly reasonable if [partners without the disorder] need a therapist of their own to help them cope."
And lastly, always support your partner seeking help, just like Douglas probably did for his wife, Zeta-Jones.
More from YourTango: Should You Believe In Soulmates?
"What Catherine did was very brave," Rapini said, who frequently counsels couples dealing with depression-related disorders. "She must have felt deep down that she wasn't dealing well with the disorder and got help. And she obviously had a good support system in Michael Douglas, because she was able to do that."