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A good therapist will have good boundaries and certainly would not be encouraging flirting. Unfortunately your therapist has already breached those professional boundaries even by waving to you while out of session. You don't need to know her sexual preferences either, so there are alarm bells ringing here. Therapy can be about anything that troubles you but you need a therapist that you trust and feel safe with. Please look into getting another therapist as the outlook with this one is not good.