Hello. Maybe you could explore the source of these thoughts, or the cause of these thoughts, with a counselor? Or maybe as soon as you become aware that you're having those thoughts/fantasies, let them go, nip it in the bud, focus on something productive. I'd say it's fairly common for people to have intrusive types of thoughts that they'd never want to share with anybody, so don't feel too alone with your issue. It's solvable.