I've never had a T that sexualized my therapy (had one who did a lot of gaslighting in other ways). But based on my experiences in other relationships that were not supposed to have anything sexual/romantic, where people did this, it was exactly like you describe in the OP. I would say that if you have this recurring feeling and perception, it is probably not unfounded. In my case, I could resolve it a few times simply by not reacting to those subtle (or less subtle) attempts at all. Other times I would just tell them straight that I don't like that behavior and have zero interest. People might try a few more times but then often give up in the absence of reinforcement and then we could continue with the real focus of the connection. I imagine there are people so aggressive/obsessed that they won't give up, but that is extreme. The problem is more when you respond/engage/allow it, that reinforces their motives.
In the case of a therapist - has he been useful to you at all? If not, I would definitely dump him. If he is useful in other ways, maybe the above strategy and stay firm and uncompromising with it.