Seems like you are the ideal consultant for this! How do you deal with emotional intensity without swearing? Just do the same for your characters.
People do not have to curse, they can sob, scream, grimace, gesture, sigh, or be articulate and say extreme things.
You can use euphemisms, as well. You can use implication: "We slept together last night" implies intercourse, you don't have to say "we fucked last night."
Or, finally, realize that every author writes evil characters doing things they would never personally do. I've written about a woman that intentionally killed dozens of people, because she thought it was justified in a greater good. She used any kind of subterfuge to get close to them, including seducing them and having sex with them.
I never have and never will do that, but I think I wrote her character convincingly.
Your story will not be good if every character is just a reflection of you. Realistic characters swear.
That said, if your story is set in fantasy world, you can invent your own swear words, that are not swears in the real modern world. That might be a route to explore.