On the Stoic idea that our emotions are under our control, from Margaret R. Graver's Stoicism and Emotion:
"We can see, then, what it has to mean for a Stoic to assert that emotions, like other hormai, are volitional or in our power. The assertion of Zeno, reported by Cicero in Latin translation, that emotions are voluntary (perturbationes voluntarias esse) is equivalent to saying that emotion events are in our power precisely because they are also assents, judgments with a certain content. As Zeno also says, they are `experienced through a judgment of opinion' (opinionis iudicio suscipi). For assent is regulated by characteristics of persons, above all by prior beliefs a person holds. The Zenonian expression is repeated many times in later sources, often paired with `through judgment' or `through opinion.'
A not uninteresting question for the history of volitionalism concerns the Greek expression Cicero is rendering by the Latin word voluntarias. The early Stoics knew and used the `up to us' formula favored by Aristotle (eph' hēmin), and Latin voluntarius could be used in an equivalent sense. I am inclined to think, though, that voluntarius here and in similar contexts in both Cicero and Seneca actually represents prohairetikos in early Stoic texts, just as it does in Cicero's translations from Aristotle. It has often been claimed that prohairetikos is not attested in the early Stoa, though it is used frequently by Epictetus in the later period." But there are traces of a Stoic usage both in the Herculaneum papyri and in verbatim reports by Origen.' In attaching this term to the pathē, the Stoics were making the most explicit claim they could make about responsibility for emotional experience."
Margaret R. Graver. Stoicism and Emotion (pp. 65-66). Kindle Edition.