Nicky was a priest or a monk or something religious, which means he more than likely took a vow of chastity. Now, after the long road of their relationship and working together and falling in love, after being chaste for however many years (I imagine Joe also didn't really partake in sex on their travels in this) Nicky finally comes to the conclusion that he's ready to give up his vows for Joe.

Joe has been patient the entire time; however long the anon wants - years, decades, centuries and is surprised by this fact but is more than happy to deliver.

Cue the most romantic lovemaking you've ever seen.