Meaning of "decades elsewhere"?

Hello everyone. I am reading a novel, and I came across this expression. Could you please let me know its meaning?

I remember the care with which he laid them out one by one on the sideboard in the dining room, cleaning and polishing his huge collection of antique corkscrews and foil cutters, Mother saying in front of everyone he reminded her of a mohel laying out his tools for a bris. Last time I laid out my tool, tell me, where, in which land that was—Someone immediately interrupts and cracks a joke about Abélard’s tools and Abélard’s love. It was Héloïse did the deed, I know wherefrom I speak, my father says, Héloïse and wedlock. Laughter, laughter, and all the while we’re laughing together, there she is two-timing him, while sorrow addles his heart for someone he’d met decades elsewhere, a love most chaste.

- André Aciman, Eight White Nights, Eight Night

This is a novel published in the United States of America in 2010. This novel is narrated by the nameless male protagonist who meets Clara at a Christmas party in Manhattan. Now the protagonist is thinking about his late father, how he used to joke about Abélard and Héloïse.

In this part, I wonder what the underlined expression means.

As far as I know, "decades" is time, and "elsewhere" is place, but I am not sure what it means when "decades elsewhere" is combined together. o_O

Thank you very much for your help.