I've been married for 23 years and love my wife more than ever. I have friends who have been divorced as well as many who are in long term marriages. It is all or nothing thinking to set the choices up as bad marriage or cohabitation. If Ms. Phillips were to do a thorough investigation she would find that the literature from the field of psychotherapy is replete with the negative impact which children experience when their parents separate whether they were ever married or not. It is extremely naive to think that issues such as custody, finances, support, etc. are going to be easily worked out because a divorce isn't needed.
Closure can also be very ambiguous as well.
The emotional impact is painful. Cohabitating partners who have built a life together soon find that they face most of the same issues as divorcing couples complicated by the ambiguity of the relationship. I realize that the people I serve as a therapist are a self-selected population. But within that population it has been my experience that women come out on the short end of the stick in ending cohabitation. It is extremely difficult in many of the 50 states to equate the rights she should have with what is established by law in the case of divorce.