problemeowtic

You can disable autonomy for masturbation so that only you can trigger it (shift+click -> configure mod settings -> devious desires -> global settings -> sex settings -> autonomy settings). Though, if it's activating so frequently then you may need to take a look at other settings. Does your sim have the "Needs Sex" buff? If so, their arousal is high and sims will seek sex interactions autonomously above 75% arousal by default. Arousal is lowered by having an orgasm, so it could be that your sim isn't reaching orgasm when they masturbate. Fiddling around with animation settings (configure mod settings -> devious desires -> global settings -> sex settings -> animation settings) should fix that. There are a lot of ways to alter the settings, so you'll have to find one you like. Personally, I set the duration to max and have "end sex after all sims have had at least one orgasm" checked.