I found this note of relevance on a bariatric surgery web site:
Dramatic weight loss in a patient will affect all interpersonal relationships, but the marital relationship is one of the most significant. In fact, a very high percentage of WLS patients get divorced within the first two years after weight loss surgery. The patient generally becomes more outgoing and socially involved as weight loss progresses - in some cases this creates a crisis in confidence for the spouse, and in other cases the patient desires to leave the marriage. We do not have a solution to this problem, except to strongly encourage patients and their loved ones to consider the upcoming stress before surgery. The marriage appears likely to survive in most cases where the patient was of normal weight at the time of marriage; however, if the marriage is not a strong one, the couple should engage in marriage counseling before the weight loss surgery. Other interpersonal relationships can experience unexpected changes as well. More than one mother or child of a patient has expressed regret over the loss of “the person they knew.”
San Antonio Bariatric Surgery - New Dimensions Weight Loss Surgery - Side Effects