I don't think I explained what I meant about figuring out what was appealing about the fantasy well. It's hard to think of a family-friendly way to put it.

Some fantasies are attractive because they involve certain power dynamics or a sense of taboo. If OP can identify exactly what it is about the fantasy that is appealing (being a temptress may be one aspect), there may be a way that she can incorporate that into her life with her boyfriend. Sort of trade one fantasy that's slightly disturbing for one that is more mutually enjoyable.