A long-term arrangement is dependant largely on the chemistry between the two parties.
The factors that govern this decision (whether laid out in the beginning or after some time spent in the relationship) can vary greatly. If the arrangement itself offers a sense that both parties interests are taken care of, then the Successful and Attractive might want to consider turning it into a long-term arrangement to maintain that sense of security.
Carl had never married. An attractive bachelor, he often caught the eye of younger women. While he had no interest in starting a family or living with someone, he liked the idea of having a casual relationship with a beautiful woman. Carl found Seeking.com and was introduced to Pauline, a beautiful young college student who was looking for a long-term arrangement with an older man. After deciding on terms that would satisfy them, they were content with pursuing a relationship that would last through graduate school, an arrangement that benefited them both.