Since dreams allow for the free exploration of feelings, it is common to dream of sharing affection, sex or intimacy with people other than your mate. As you ‘role play’ by experiencing the different aspects of yourself, it can be portrayed by various characters, where you sometimes behave in a masculine way (mounting/dominating) another masculine character (your aggressive and assertive nature.) You are merely exploring your desire to be more aggressive.
You may dream of being unusually sensitive or affectionate with another woman, or in a feminine way, as a way of ‘embracing’ or exploring the idea of increased sensitivity within you. The side of you this person represents and how you approach them in the dream, will feel ‘clandestine,’ only in proportion to how you are currently not ‘embracing’ or integrating this side of yourself in waking life. See Anima/Animus and Archetypes and Universal Characters.