I think it depends what someone is going for. If they are specific things that can be set as goals, the goals are met and no new need comes up, it may be a good time to move on. As far as I can see, many people see Ts driven by more diffuse needs such as general support or to work on very complex issues that do not only affect one behavior or emotional area. That way it is hard to define it, I guess it's more a general feeling when the need is resolved and dissipates.

I also personally think it can be a good time to be done when the therapy becomes too much the center of the universe for someone, too much of an obsession, and someone neglects other things due to it. This does not seem to be the case for OP though.

I don't think it is always best/necessary to terminate therapy over a few sessions, really depends on what the client likes. What I don't think is when Ts try to tell the client how they should terminate. One of mine tried to manipulate me to go back just to talk about my decision and I regretted when I did because it just brought up a bunch of unnecessary and irrelevant (to my life) annoyances.