Some states recognize common law marriages. So, it depends upon where you live.
Actually, there is no definitive time period to establish a common law marriage in those jurisdictions which recognize them, and it cannot happen by accident. There must be (1) An intent to be married; (2) the couple must hold each other out as husband and wife. This can be done by the wife taking the husband's last name, or referring to him as her husband. Finally (3) the marriage must have been consummated. If/when these requirements are met, then there is a common law marriage which is every bit a marriage as if it were celebrated in Westminster Abbey. By the same token, if one enters into a common law marriage in a state which recognizes the same, under the Full Faith and Credit Clause of the Constitution, the couple are legally married in all 50 states. It can only be dissolved by divorce, not be separation alone. Similarly, if one is a common law spouse, one is entitled to the same inheritance as if the marriage had been celebrated by an officiant. So, the issue here is not the length of time, but rather if the couple intended to be husband and wife, and if they lived in a state which recognizes common law marriages. If the answer to both questions is yes, then the surviving spouse is entitled to a spouses share by law. If the answer to either question is no, then the survivor can only survive if the decedent left a valid will with a specific bequest which will withstand challenge.
I would say no. I agree with post 4 that even a common law marriage isn't likely to overrule a proper will. To my knowledge, common law marriages laws are mostly written about a couple who has lived together for a long period of time and breaks up while both parties are still living. They were designed to ensure both partners had equal rights to shared assets. The laws surrounding a deceased's property and their will are very different. In some cases, even spousal privileges cannot override a will. In my experience, common law marriage laws, the rights of a spouse, or the rights of a girlfriend are likely to come into play only if a will does not exist.
I am not sure if a common law marriage law would override a will. If the boyfriend has a will that specifically leaves everything to his children, you would have to fight the will in court to argue the common law marriage entities you to something. You might even need to prove that your own property is yours.
State laws will vary widely on a question like this, but in general, there would be no entitlement to a boyfriend's estate unless the boyfriend had provided for it in a will. Some states and countries do allow common-law marriages, which would give a spouse legal rights without having done an actual wedding ceremony.
It primarily depends on what state you live in and what the laws of inheritance are in those states. Some states recognize common-law marriages in which a female has lived with a male for a certain period of time and that female is considered a wife and entitled to certain benefits and responsibilities. Generally, a probate judge decides the boundaries of the relationship and the disposition of someone's estate.