Your epithalamium is showing

Adam O'Riordan takes Guardian readers on a tour through epithalamia (no x-rays or invasive surgery required.) Though it sounds more like an obscure piece of anatomy you never knew existed until you embarrassingly managed to strain it while mowing the lawn, the epithalamium is "a handsome but disconcertingly formal word meaning simply a poem for a bride or bridegroom, from the Greek 'thalamos' or 'wedding chamber.'"

Citing John Donne as the most well known composer of these (usually) celebratory verses, O'Riordan offers comfort to those who find the institution of marriage less universally joyful—perhaps strange, worthy of subversion, or needing an outsider's perspective in the form of the unrequited lover. Running through a survey of wedding poems by Seamus Heaney, Roddy Lumsden, Louise Glück, Sappho, Michael Longley, Donald Hall, and Sir Thomas Wyatt among others, he finds a surprisingly wide range of variations on the theme:

Poetry has an ability to invest ceremony and exchange with a deeper meaning, but it can also subvert their value. In Third Day of the Honeymoon, Jean Sprackland has a new wife lose her ring in the sea, only for her husband to tell her: "Never mind, I'll buy you another. / For now, she's properly naked at last." Meanwhile, Jacob Polley's brooding, Gothic Dor Beetle declares: "Scavenger on slug flesh, shit-eater, / I wear you on my wedding finger", demanding: "At the end of love, start burrowing."

Poetry can destabilise, emphasise or simply make us reconsider the value of customs and traditions involved in a wedding. Nick Laird's Estimates, from his collection On Purpose, offers a compelling alternative to having "two hundred friends to watch / you wear the white and walk the aisle". The voice in the poem suggests they "motor north" and "pull in somewhere … kill the engine, wait, listen / to a late-night country music station, / split bars of dark and fruit-&-nut, sip amaretto from the lid, skin up, and wake unwashed and cramped / as man and wife".

As to the question of why poetry and marriage are so often linked, O'Riordan makes a proposal of his own:

It strikes me that both the act of reading a poem and the act of marriage are in essence a decision to take certain words seriously - and both require a degree of faith.