idk if this helps you but jack wanted elizabeth to be a pirate and elizabeth wanted Jack to be courages! then the story about a widow with her husband lost at sea! Jack proposed to elizabeth but meant it figuratively not literally little did he know that they both met each others wants making them their vows then jack dies which ties in with widows husband lost at sea jack died in the sea, making elizabeth a widow so they are kinda married but not so literally.
I can see Jack getting married i know some people think "oh he's a pirate it doesn't fit in very good and jack doesn't do that sorta thing!" Jack has done many things we never think he do: he fell in love, he told the truth, he did something courages, he gave up his ship to the kraken. I think when jack said his first and only love is the sea and how he doesn't want to make elizabeth and obligation he does just that he knows he has fallen over heels for her (sorry for being so romantic i just watched the holiday) he does make her an obligation and in the end of DMC we saw jack as a new man i really can see him getting married to elizabeth and sailing togteher wherever they want no rules no bounderies just them the crew and freedom. idk if this makes any sense to you i just had to spill it out and in my mind it makes sense.