awful sex dream (nightmare) about ex

i recently had a dream where i had sex with my ex. i woke up feeling slimy and disgusting.  he led me on for around five years, two timing another girl and i. i know it sounds silly, but it made me feel like i cheated on my current boyfriend, even though i obviously didn't (😂). i haven't spoken to my ex in over 8 months, and i always try my hardest not to be bitter about what he did to me, and i thought i was over it! but i guess my subconcious thinks otherwise... 😕 any advice on letting go?