No, it's a pun. You see, there are three of them: Michael, Steven, and Stephen. All in a group wedding. (The fact that they all look the same threw you off.) Thereby forming a menage a trois. And if it were a lesbian wedding, it would be a womenage a trois. And you could have also been a twomenandaladyage a trois or something.
Then there's always the manwomanpetpaperclipandcthulhuage a cinq ...
[Click to view comic: 'CC 127: Non-Traditional Marriage']
As proven by the hilariously funny umfumdisi.
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