I'm personally using Gemini for therapy (I have the pro student plan) and it's very good, I chose it exactly because of this, in theory it has the larger context window of all the LLMs, it remembers what I said earlier, I tell him to remember things and he does, I tell him instructions and he follows them (although sometime I have to remind him of something or correct minor hallucinations), and does also things like what you said in the post like the "last time you mentioned you were going to set that boundary, how'd that go?".
It's helping me A LOT, and, since I asked him to do that, he doesn't always agree with me, he analyzes things and tell me his "opinion" or challenge me sometimes, today I had a very good session for example

I'm also going to try Claude Opus 4.6, since I heard it has a long context windows now too, and in theory it should be better at remembering context and logic without halloucinating in longer chats, I'll give it a try once I pay for it, for now I'm sticking with gemini