This is a charade - multiple parts are joined together in sequence to build the answer word by word or letter by letter.
Take the beginning letter of 'introduce', add a glimpse (first letter) of 'billy', then follow with what 'once partner' means (a former romantic partner). Put these pieces together in that order.
Answer: IBEX | I (beginning of 'introduce') + B (glimpse of 'billy') + EX ('once partner' meaning former partner) = IBEX (a type of wild goat)