UPDATE:
You guys were all right - staying at Nottingham was the best for me. Problem is, I was just so focused on uni, education, rankings blah blah blah, and had not considered my wellbeing at all. I have been and am struggling alottttt with mental health, and I hadn't considered the toll another period of instability would take on me. I was far too focused on trying to correct the past or how I'd feel in the future, that I didn't consider how I felt right now. Basically, I've ****ed everything up. I'm not allowed to go back to the subject I was studying last year - instead I've been forced to start a whole new subject. My mental health is dog ****, and I can't bring myself to study or see friends or play sports or participate in societies. Everything is ****.
The department of my old subject won't let me back in, I tried to cite my mental health as a concern, but they don't really care - they're no longer even responding to my emails. They said in a meeting that they are not obligated to help me (this is true - uni policy states it is at the discretion of individual departments whether or not they allow students to study that course). I feel stuck. I want to make the most of my new course, but like I said, I'm just not doing well mentally because of all the turmoil and instability. I might now have to interrupt my studies since I'm so behind on work, and though I'm trying, I just can't bring myself to do anything anymore.
My priority has changed completely - before it was all about uni choices, now, it's about trying to preserve my mental health. And if I'm honest with myself, part of that is to not subject myself to anymore change or to another round of applications, open days and decisions. I just need some stability. But the chance for that seems to be gone. I wish the old dept would consider my case but they're being very clinical and are all about the bottom line, which is that I chose to leave. The new dept have been very supportive, and are trying to help me. But again, I just can't deal with this change and instability right now. I think I'm going to have to interrupt and return next year, but I still won't be allowed to study my old subject - they basically said to me point blank in the meeting that if I wanted to study that subject, I'd have to go to a different uni.