(LifeWire) -- Relationships are tricky enough with just two people involved so imagine how delicate the balancing act becomes when your ex is still in the mix.
"When you have an intense relationship, there is a danger that you won't move on or let go," expert warns.
Rob, 31, a mobile technology entrepreneur in San Francisco, has already lost one girlfriend because of his ongoing relationship with a former flame -- who also happens to be his business partner.
"We're like Jerry [Seinfeld] and Elaine," says Rob, who didn't want to be identified by his full name because he's in a new relationship. His shared history and intimacy with his business partner help them sizzle on sales calls, but it also made his then-girlfriend see red. "It was really hard for her," Rob says. "It was a strained relationship that wasn't going to go the distance."
Whether it's because of work, children or difficulty letting go, exes are a fact of life for many couples. Even if you try to shelve differences and remain friends, is it possible to be too close to an ex?
"You can be too close if it's creating problems in your relationships or if it's preventing you from moving on with your life and your work," says Gloria Fraser, a psychotherapist and mediator in San Francisco. Close relationships cause conflict for some, but "if it works and everyone is having a good time, then why not?"
Make that ex-roommate, too
To maintain the right balance, Fraser advises setting boundaries. That probably includes not living together.
Mary, 33, an office manager in San Francisco who did not want her real name used to protect her soon-to-be-ex-husband's privacy, has been separated from her spouse for four months. But a tough rental market makes it difficult for her to move out and move on.
She says their proximity occasionally causes flareups of jealousy: "It's hard to hear from mutual friends about him being with other girls, or if I see a phone number of a girl on a bar napkin in his bedroom." And it's discouraging her from seeing other people.
"We spend hours talking," Mary says. "But friends tell me that I need to stop having contact with him."
Fraser agrees. "When you have an intense relationship, there is a danger that you won't move on or let go," she says.
For Andy Griffiths, a 43-year-old architect in San Rafael, California, that's not an option. He's raising his 12-year-old son with his ex-wife after an amicable divorce, and they've decided it's important to continue their annual family camping trip to Yosemite.
The first year, it was just the three of them. The next year, his ex-wife brought her new boyfriend. The following year, both brought significant others.
"It was a disaster," he says. "My girlfriend was sensitive to the posturing and comments of my ex. To have that much face time and share three meals a day and hear stories about what happened in previous years at the camp -- it was upsetting for her."
Griffiths and his girlfriend are no longer dating.
Bill Ferguson, a former divorce attorney who now counsels couples on divorcing amicably or resolving conflict, doesn't believe it's possible to be too close to an ex, especially when children are involved.
"The healthy thing (for a new partner) would be to encourage someone to have a good relationship with their ex," says Ferguson.
But Fraser says it doesn't always work that way, because the new partner tends to worry that the person hasn't gotten over the ex. She says it's not important that jealousy is unwarranted -- "what matters is that a partner is feeling distressed, and hopefully their partner will do what's needed to help them feel comfortable."
The ex can help, too. Rob is in a serious relationship with someone new, and Danielle Benakos, Rob's business partner and former flame, says she goes out of her way to make Rob's current girlfriend feel comfortable with their unconventional dynamic.
"It's what any nice, confident normal person would do. And... it's what my mom always told me to do," Benakos explains.
Good for the kids
This year, Griffiths is bringing someone new on the Yosemite trip, but he's more optimistic this time: His girlfriend also shares custody of her children with her ex.
"You'd think I'd learn my lesson," he says. "But if she can handle this, she can handle anything."
It's worth trying. Studies show that children adjust better when their divorced parents remain friends, Fraser says. That was a lesson Dennis Kelly, a software executive in San Francisco, had to learn the hard way. After a tumultuous divorce, he observed in his then-9-year-old son "deterioration in his demeanor and a little fear."
So Kelly learned to work on himself, and even said a few prayers. Over time, he's shed the animosity and blame.
"It made it better for myself, for my son and for everyone else," says Kelly. "If you focus on what's best for the kids instead of each other, you do the right thing." E-mail to a friend
LifeWire provides original and syndicated lifestyle content to Web publishers. Liane Yvkoff is a freelance writer in San Francisco.