When to stop?
The short answer is: When you want to.
Once the symptoms that brought you into treatment have abated, then its a matter of choice whether or not you want to continue exploring and improving your life through psychotherapy. Some do, some dont. [Chris, Ed, Jim] There are only a few other considerations.
Sometimes there is little or no doubt that you should change therapists. If your therapist wants you to have sex with him, wants to borrow money from you, or if he commits some similar breach in the appropriate boundaries of behavior, dont stop and think; just get out. You do not need to have a beer with your therapist, visit his country house, go to the opera with him, or hear about his personal life. The only time the last would be appropriate is if he is telling about himself to help you understand your own life. The minute youre bored or lost, speak up.
In general, it is time to move on when you cannot talk about something. Your therapists office is the one place where you must be free to talk about anything. Thats what you pay him for. In fact, a major part of his job is to help you talk about difficult subjects. So if you have some discomfort or gripe with your therapist, you should be able to bring it up and reach some resolution and understanding. Of course, you have to make that effort, but if you do and you get no satisfying response, it is time to find another therapist.
Also as a general rule, I think you should be wary of therapists who give advice, particularly early in treatment. The worlds full of advice. One of the reasons you come to therapy is to sort out your own priorities and interests from all the advice around you; the last thing you need when youre lost or stuck is yet another opinion to weigh. The only exception to this is the case where you are simply not functioning [Patrick].
Be clear on the difference between advice and other kinds of input. If a therapist tells you that your attachment to your current lover sounds to him like it is based on your love of escapism and not of that person, and thus to stop and think before you set the wedding date, that sounds like fair game to me. But no therapist should be telling you flat out who to date, marry, travel with, etc. What you want is for your therapist to help you consider your rationale for those choices, to get you interested in sorting out real world considerations from inner, psychological, motivations in those decisions, not for him to take over for you.