Amor non est passio laesiva, sed magis conservativa et perfectiva, quia amor significat coaptationem quandam appetitivae virtutis ad aliquod bonum; nihil autem quod coaptatur ad aliquid quod est sibi conveniens, ex hoc ipso laeditur: sed magis, si sit possibile, proficit et melioratur.
Love is not a wounding passion, but rather one that preserves and perfects, because love denotes a certain fitting adapting of the appetitive power to some good; but nothing is hurt by being fittingly adapted to that which befits it: rather, if possible, it is perfected and bettered.
Et hoc quidem dictum sit de amore, quantum ad id quod est formale in ipso, quod est scilicet ex parte appetitus. Quantum vero ad id quod est materiale in passione amoris, quod est immutatio aliqua corporalis, accidit quod amor sit laesivus propter excessum immutationis: sicut accidit in sensu, et in omni actu virtutis animae qui exercetur per aliquam immutationem organi corporalis.
And let this be understood as applying to love in respect of its formal element, i.e. in regard to the appetite. But in respect of the material element in the passion of love, i.e. a certain bodily change, it happens that love may be hurtful, by reason of this change being excessive: just as it happens in the senses, and in every act of a power of the soul that is exercised through the change of some bodily organ.