c. 1200, affeccioun, "desire, inclination, wish, intention;" mid-14c., "an emotion of the mind, passion, lust as opposed to reason;" from Old French afection (12c., Modern French affection) "emotion, inclination, disposition; love, attraction, enthusiasm," from Latin affectionem (nominative affectio) "a relation, disposition; a temporary state; a frame, constitution," noun of state from past-participle stem of afficere "to do something to, act on," from ad "to" (see ad-) + facere (past participle factus) "to make, do" (from PIE root *dhe- "to set, put").
Sense developed in Latin from "disposition" to "good disposition, zealous attachment." In English the sense of "love" is from late 14c. Formally it goes with affect (v.2), but it has absorbed some sense from (v.1). Related: Affections.