nemo
What a lovely pun! I didn't know the poem, although I have heard the last 2 lines occasionally. I suppose that Sally could not wait for years, and the romance might not have continued anyway. Nowadays a girl might.
I imagine the poet wanted it pronounced boatswain rather than bosun, but perhaps bosun in an earlier line.
Interesting, perhaps somebody (ChrisE ?) could tell us.
If it is boatswain, I would be pleased as that is how I used to pronounce it.