While it may be accepted by your friends and perhaps even your family, it is still not fully accepted under the law.
If the unmarried parents split up, the father has no automatic legal obligation to support the children, let alone the mother. And the father has no legal right to visit his children, or even to know how they are doing. This can only be changed if the parents go to court for a hearing before a judge... and is a good deal more involved than getting married would be. (Unfortunately for the men who think avoiding marriage can avoid child support, the mother of a child could still go to court to collect child support, including back child support, several years later, and a court could stick the father with an order to pay tens of thousands of dollars... even if the father has not seen or been allowed to see the children in years.)
(Just in case you consider your decision to live together as sort of a "trial marriage" to see if things "work out" and if you are "compatible" so you don't get divorced after encountering problems you did not expect... you might also be interested in knowing that couples who get married after living together end up being more likely to divorce that their counterparts who never live together before marriage. In other words, if you want a marriage to last, get to know the person, but do not live with them first.)
Insurance companies won't give health insurance at family rates for a live-in partner, and usually won't provide coverage on the same policy at all. Social Security death benefits are available for a widow or widower, and for the children, but not to a live-in partner... and the father's illegitimate minor children will also have a great deal of trouble getting death benefits in his name after his death.
The law of inheritance also has a very strong bias for marriage. A widow or widower has an absolute right to a portion of the estate, but if you never married the father (or the mother) of your children, you could end up with nothing, and it is certain yo will end up with nothing if there is no will. It's also much more difficult for children to inherit from their father if the parents were not married.
Even getting in to see a the person you love if they're in the hospital or in jail is a great deal easier if you're legally married.
Some couples don't formally get married because they hope to avoid the trouble and costs of divorce. But ending a long-term living together relationship, and dividing the debts and belongings, can be every bit as messy and involve as much time in court as a divorce.
But what about common-law marriage? Tennessee does not recognize it.
If you make the decision not to get married, at least think about the consequences.
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