We have several types of interpersonal relationships, parallel to Marriage, as provided by the Law in Italy.
§ Let us leave aside the case of Civil Unions: these are simply the equivalent of marriage for same-sex couples who will need a formal divorce to dissolve: we will concentrate on the non-ceremonial unions between heterosexual parties.
§ This type of “sui iuris marriage” can be registered or unregistered, and may imply the stipulation of a cohabitation agreement regulating many things, such as property matters and other financial and non financial matters like support. For instance, if you are a sole owner of a property, and intending to allow others (e.g. an unmarried partner) stay in your property, this is a way for you to set out the rights of that other person in relation to their financial interest in your property. The members of these couples, albeit not wishing themselves to be considered by the State as a married couple (otherwise they would probably marry) can claim some rights which are similar to those of a married couple when the cohabitation ends.
§ As to registered cohabitations, the numbers in Italy seem too tight to even mention: in fact, the purpose of a cohabitation is precisely that of NON being considered by the State as a married couple. Therefore the registered cohabitations since their introduction in Italy by L. 76/2016 did not make a big success: in the absence of a National Statistic, we know that large italian cities have counted only a small number of registered cohabitations in the first years of application of the new law. https://www.ilsole24ore.com/art/coppie-fatto-due-anni-via-registro-comunale-non-decolla-AEMxe5pE
§ As some may know, a marriage (rather: the dissolution of a marriage) in Italy does not bring automatically the division of family assets: there are many exceptions to the communion of assets. First of all, the spouses may choose the financial separation of assets, when wedding: this formal agreement will separate the fortunes of either spouse for a lifetime. Moreover, regardless of a “financial regime of separation” as it can be chosen by the spouses, a number of circumstances may leave the property of assets intact in the name of the sole owner in case of divorce. Finally, aside from the choice of a separation regime, no other prenuptial agreement is admissible in Italy. In other words: the very idea of marriage as a partnership of equals, which is typical of Common Law Countries, is totally unknown in Italy.
No wonder, a fortiori, that the end of a cohabitation has no effect whatsoever on the parties’ finances in the absence of written formalities. Outside of marriage (with the exceptions considered above) there is no automatic right to home ownership, even if the home is shared for a long time.
§ The most interesting innovation of the Law 76/2016 is that of “alimonies” that Art. 1 comma 65 provides in case of dissolution of a de facto relationship. Alimonies are a form of minimal support owed to a relative in need. Art. 1-65 L. 76/2016 is introducing the idea of alimony owed to the ex (informal) spouse which may vary depending on the duration of the partnership.