I like your honestly @
throwawayhighdog I am female and I gave myself a lot of guilt for masturbating when I was younger (I am now 54). I grew up Catholic and was told it was a sin, a point of view I now disagree with vehemently.
You are not a bad person for masturbating as much as you want, or for having fantasies. If something arouses you I don't see why you shouldn't think about that. It's just thoughts. That said, if it is really bothering you I would suggest talking to a professional counselor/therapist. You might want to look up the clinical definition of addiction because I'm not sure your activities would qualify.
Sometimes a sexual thing is appealing precisely because it is "forbidden fruit" and thus seems shameful. If you accept that you have this fantasy for a psychological reason, you might find its grip lessens.
Take care.