I think MKAC's theory makes a lot of sense. My T has offered to extend my appointment maybe 3 or 4 times, and the first time I had a fair amount of difficulty with it. I have only stayed about 15 minutes each time-- or maybe 20, if you count that he had no break at the top of the hour. For me, that was more about I just can't dig into stuff that is tough for that long. I sometimes leave 5 or 10 minutes early as well.

I know you get intellectually that someone inviting you to stay is not the same thing as breaking a time boundary. You aren't grabbing onto your seat saying I refuse to leave, so you're not like your mother or anyone else who routinely pushes over people's limits. He is asking you to stay, which isn't even him breaking his own time boundary. It is like he is stepping into (as are you) an entirely different setting with a new boundary, which is 50 minutes later to be technical about it.

For me, and I think I have written about this recently, it is also about learning to accept what people offer me, being comfortable with that, letting go of my need to be so determinedly independent. I don't know how you were as a child, but I was the queen of "do it myself". I worked really hard to do everything and not ask anything of anybody. I knew that my father (who loved to help) could be manipulated by simply allowing him to help when it was strategic for me. I would only allow him to help if I needed or wanted something from him. Usually I didn't need his help on the homework or whatever it is he was interested in. In this way, declining people's help for me was a way of keeping them at a distance, or manipulating them for my own gain. I'm not too proud of my manipulation-- but I look back on it as a tool in a family situation where I usually didn't have much control. So I took the control when I could.

For me, I am also cognizant of not wanting to "use" other people's help as manipulation-- I think that I must be still inclined to do it, because I did it 30 years ago. So I err on the side of declining help because that allegedly protects me from myself. It may just be another way that I make excuses for pushing people away.

I'm guessing that you'd like to change how this kind of thing goes down, in some near or far distant future. Can you work on accepting help from others or T in smaller ways that don't have to do with perceived boundaries, and see how that goes (or maybe this isn't an issue for you?). Is this also about rigidity, wanting to be able to change your response, in which case you can work on making steps in that direction (such as desensitizing your reaction to this situation, in whatever way you have desensitized yourself with previous triggers)?

I think in general, when we become less rigid and more flexible about what we can do (if it's something we want of course, this doesn't apply if you don't want to be able to accept additional T time), it increases our general healthiness, because we can now choose what response we will engage in during that moment (accept or not) rather than following that well worn groove of how we "must" behave.