Margaret R. Graver's Stoicism and Emotion tackles the difficult issue of the complex idea we call "love" in the context of Stoicism. As she writes, there is reason to wonder whether it counts as an affective response at all:
"Given that wise erōs is not a form of desire, there is some temptation to try to classify it with action tendencies of the calm `selective' type and to conclude that the wise person is devoted to erotic activities only as preferred indifferents, in about the same way as he might be devoted to studying literature or hunting with dogs. Against this it should be noted that the object toward which this love is directed-that is, the forming of a friendship-is an object the wise person recognizes as a good, albeit a good which is to be realized at some time in the future. This is the primary mark of a specifically affective response, as opposed to a merely `selective' impulse, that it depends on an evaluation of the unconditional sort. For this reason alone we should not hesitate to interpret Stoic erōs as having a place among the eupatheiai. As a future-directed eupatheia, it can be classified as a subspecies of wish (boulēsis), alongside the friendly responses of good intent, goodwill, welcoming, and cherishing."
Margaret R. Graver. Stoicism and Emotion (pp. 187-188). Kindle Edition.
In other words, love in its purest sense is not a passion, involving an incorrect judgment about another person or a situation. If it turns into an irrational over-valuing of another person or relationship, than it becomes a passion we suffer. But if it is a rational judgment followed by rational and friends responses of well-wishing, that is not a passion, and can be - nay, must be - indulged by the sage.
Some more thoughts on the positive purpose and outcomes of love follow. According to one analysis, the Stoics, especially Zeno, conceived of "eupathic love as having an educational purpose; that is, that the wise lover's wish is not only to form a friendship with a young person seen as potentially wise but also to supply whatever teaching is required to realize that potential. That eupathic love should foster educational endeavor is an attractive hypothesis, especially in view of the age difference between the lover and the beloveds' In view of the Platonic parallel-for Diotima in Symposium 2o6c-2o7a is similarly concerned with intellectual reproduction-we are probably justified in finding this thought in the remark in Stobaeus that erōs is "a protreptic toward virtuous matters." If Zeno thought that love relations between the wise and younger persons who are not yet wise would encourage the latter to study moral philosophy, then it is easy to see why he would have held that love "contributes to the security of the polis." The `security' would then mean sure continuance over time, as each wise person is moved to train one or more younger persons to replace him.
But we should be careful not to conclude that the educative dimension of the love relationship is what justifies wise erōs in the eyes of Stoics. Erōs does not require justification; it is a good thing in its own right, as are all the eupatheiai. The wise fall in love for no other reason than that it is their nature to want to be intimate with those whom they see as beautiful. A wish to impart wisdom might be part of their endeavor; how could they not want the beloved to acquire what they value for themselves? But it is the intimacy itself that is their object."
Margaret R. Graver. Stoicism and Emotion (pp. 188-189). Kindle Edition.