I fell in love with a girl
O and a gash
I'll bet she now has seven lousy children
(I've three myself, one being off the record.)
I wish she'd read my book & write to me
“Gash” is slang for the vagina. The context suggests other metaphorical possibilities as well: that the girl represents a psychic wound for the poet, that he cherishes that psychic wound, etc. The line is a blunt, cynical comedown from the one before, and the rest of the stanza follows in that style.
Her  It