Open House by Elizabeth Berg

Samantha Morrow's life is turned completely upside down when her husband of many years decides that he is leaving her. Once he leaves her, he announces that he will cut her off from any financial help he is giving her. Realizing that she needs to find someone to keep her house for herself and her son, she finds a roommate who helps with the bills. Samantha also tries to find a job but is stuck will small, petty jobs without any real substantial income. When her housemate moves out, Samantha desperately tries to find someone else to help with the mortgage and allows a college student to move in.