Dream interpretation varies so much that it is probably not possible to get at what it "really means" without a lot of background and probing so talking to your therapist about it is the best way to get help understanding it, especially if you find it disturbing or connected to something shifting as you say.

Some say that everything in a dream is a part of you so you may be right that it really isn't about incest. It is about something seemingly taboo though I guess I wouldn't feel disturbed by the content. I guess I expect that people's dreams and unconscious material contain lots of taboo things and that is just part of being human.

But if you have negative associations, it's probably worth exploring what those are, not necessarily the imagery and actions of the dream by itself. It sounds like you may have some more positive associations as well so seeing how everything works or doesn't with each other might tell you about whether something is coming together or in conflict.

See if there are past or current connections to things in your life. Sometimes the connections are not obvious or logical, but still are meaningful. For instance, the fact that you describe your position as passive (he is kissing you, not you kissing him) and that you are pretending it isn't happening stand out to me as significant, even more so than the kiss or his relation to you. Being open to things just coming up is generally a good way to start with a dream.