I imagine that there are a variety of reasons why a masseur might shift between therapeutic and erotic sessions (e.g., timing, relationship status, arousal, attraction). I do understand, however, that once a masseur goes erotic it can be tough to return to strictly therapeutic, as the client might take it personally. If I were in this situation and enjoyed the therapeutic massage, I would continue seeing the masseur with the mindset that extras are nice but not guaranteed.