To be on the hunt for a (usually sexual) partner.
chase one's tail
To busily try to perform many tasks or to repeatedly revise one's plan…
live with
To share an abode as an unmarried partner in a sexual relationship.
have one's way with
To engage (as the more active or dominant partner) in sexual intercour…
notch on one's bedpost
A sexual conquest; a casual sexual partner.
old flame
A previous boyfriend or girlfriend; a former romantic or sexual partne…