Update - think I’ve figured out what might be going on here, with myself anyway.
My new T introduced the concept of ‘window of tolerance’ to me; I looked it up and found an illustration saying “children who have experienced trauma/loss swing from hyper-aroused to hypo-aroused with limited amounts of time within their window of tolerance”. So, I’m thinking this is a trauma response (old wounds) and the crushes are the stimulus, because I don’t normally get the more extreme ‘mood swings’ outside of feeling attracted to someone else. I do feel afraid of losing that person, unless I don’t actually want to/can’t date them, and then my moods are a lot more stable. I’ve experienced this since I was at least 15 years old.
Hyper aroused being the very anxious state, and hypo aroused being numb/depressed/emotional flatlining.