It's probably a phase, so I think it does get better.

Acting out is part of therapy sometimes; not ideal, but it goes with the process for many of us. It's fine also because you take responsibility, so don't beat yourself up. Therapy draws out such intense emotions that you likely were not dealing with for most of your life. Trying to adapt life to these feelings is hard and takes time!

While there is a chance he filled the slot within a half hour, it seems like your therapist was doing more behavioral control than anything. I think that can backfire for several reasons. One, it shows you can sort of control his behavior. Two, it shows you can affect him. Three, it can draw you in as part of a dyad for acting out or repetition compulsion.

My view on this might be different than others, but it comes from my interpretation of a psychoanalytic bent to things, especially in terms of remaining neutral. There was a period where I cancelled my sessions semi-frequently most as a result of primal fears/fears from a young place, then soon asked for the sessions back. He just cancelled when I asked, then subsequently gave me the session back when I asked. He didn't react, didn't punish, didn't comment; although we explored the feelings behind it as they arose. That worked for us, as the urges disappeared. In fact, they really hadn't come back.

I do think it's sort of passive aggressive of him..

Sorry you are feeling bad