Husbands and wives share many aspects of their lives. It is not unusual for them to share their Facebook friends and other social media contacts. The practice of looking at someone's friends or contacts and trying to convert them into your friends or contacts has earned its own nomenclature. The UrbanDictionary calls this practice “Facejacking” (limited to Facebook), “Spacejacking” (limited to MySpace), “fooching”, "mooching," "friend poaching," "friend reaping," or "friend swiping".
Facejacking does not create problems when the couple is together. Frequently, one spouse encourages the other to do so. However, once the couple split up and get divorced, attitudes change. While the couple may
remain Facebook friends, it is not acceptable for a former spouse to Facejack the new friends and contacts and reach out to them. The last thing that an ex-husband wants is for his ex-wife to contact his new girlfriend through Facebook. This is especially bad when the girlfriend doesn't expect such a contact. The way to prevent this problem is to anticipate this when drafting the divorce agreement.
A typical divorce agreement has a clause that requires each spouse to respect the privacy of the other. I recommend additional language be added that prohibits Facejacking and the like. An experienced divorce lawyer should be able to draft language that protects both spouses equally from the ex-spouse using Facebook to try to sabotage your new relationship.