We usually think about adoption as a relationship solely between parents and children.

It's not.

Before same-sex marriage became legal across the United States, some couples would become parent and child — just on paper — to get rights they were otherwise denied.

That's what Sergio Cervetti and Ken Rinker of Doylestown, Pa., did years after meeting in the fall of 1965. Rinker was 19 at the time and just back from a trip to Europe with his student dance troupe. He says he felt invigorated by Cervetti, who was five years older and a composer.

"I wasn't seeking a partner, I wasn't seeking love; it just happened," Rinker says. "So suddenly I found this person who was, to me, making my world round again."

Two years later they moved in together.

Both have considered themselves as good as married for decades, but for most of their lives together, there was no way for them to legally become family. Another same-sex couple they knew did some research. "We were told that the best thing will be to adopt," Cervetti says.

Long before same-sex marriage, one member of a couple would adopt the younger member to confer benefits like shared health insurance. It was also a way to make sure partners would be recognized as family in the event one member became sick or passed away. Members of same-sex couples have been forcibly removed from a partner's hospital room and have been denied powers-of-attorney and other legal benefits.

So in 2000, Cervetti adopted Rinker.

"This is something we've known about for years, this practice, but there's never been a way to track numbers, and there still isn't a way to track numbers," says Nancy Polikoff, a law professor at American University and an expert in LGBT family law.

Polikoff says the practice wasn't rare; she's heard of cases around the country. These adoptions, while the best option at the time, don't offer quite as many benefits — including some tax benefits — as same-sex marriage, which is legal everywhere now.

That decision actually created a dilemma for couples like Cervetti and Rinker. In 25 states, a parent can face jail time for marrying their adoptive child.

Polikoff says almost every annulment she has heard about has gone through.

Cervetti and Rinker had no trouble convincing the courts to annul their adoption. "It took 10 minutes," Cervetti says.

Just like that, they went from legally father and son to able to marry. One Pennsylvania couple has been denied an annulment of their adult adoption; that case is going to a higher court early next year.

In July, just three months shy of their 50th anniversary, Cervetti and Rinker got married in a small ceremony.

"It was Sergio, me, the mayor and the two cats. And some champagne. And that was it!" Rinker says.

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