Green’s Dictionary of Slang

(UK society) doing good for others in the hope that one will receive equal good in return; often as a euph. for sexual intercourse.

c.1700		London-Bawd (1705) 125: My Husband’s Impotency [...] grew daily more upon him; and my desires after that due benevolence he could not give me, still increas’d.
1706		Fifteen Comforts of Cuckoldom 2: As for you / If Night and Morning some small matter do; / You think you’ve done your due Benevolence, / When I with thrice your Labour can dispence.