In our society, there is not a huge amount of difference between couples who live together unmarried and couples who have signed a marriage contract. There is no negative societal pressure; you can get a family membership at a gym or gallery; and you can be listed as parents on a birth certificate and be fully involved in your children’s lives.
Legally, however, there is a world of difference. My friends who practice family law would be able to give a full rundown of all of the ways that legally married spouses have better rights over family property, but I am going to mention only one here: only legally married spouses have a right to inherit if there is no will. That bears repeating: only legally married spouses have a right to inherit if there is no will. If you are common law, the house is in your partner’s name, and your partner dies without a will, you will get absolutely nothing. You will be entitled to sue the estate for support, but you will be automatically entitled to no part of the estate; it will go to their parents, siblings, or children, as the case may be.
If you are not legally married, especially if there are assets in only one name that truly belong to you both, you MUST get a will.