Peripheral to your second comment I recently suggested to someone having serious issues in a monogamous relationship that she look at polyamory - not that she should try it, obviously (I mean, obviously that's not something I'd give advice on, either way) but that some of the people engaged in a poly lifestyle have examined relationships and written about them in a way that I think is good and valid for any romantic relationship, mono or poly. Some of what I've read about realizing it's not reasonable to rely on one other person for all your emotional/social needs, especially, seemed very relevant to her problems. Fortunately someone else immediately chimed in, agreed and suggested some good specific examples, I think including polyamory.org.