Sorry to hear you’re on this emotional rollercoaster. I can only offer my sympathy.
And my personal experience: When I’m stressed out or overstimulated I tend to want to close off from the world. Even from my boyfriend, and especially when he’s the source of my stress. This can cause me to seemingly run hot and cold, when in reality it’s not so much the relationship I’m on the fence about, it’s more about my ability to stay in it and stay sane.
In previous relationships I’d break up with people because of an acute stressor and when I was feeling better after a few days I felt like I could handle the relationship again and I was ready to get back together. It took me some time to realize that this is not how you treat a fellow human being, so I took myself off the dating market and started seeing a therapist instead
I still notice these sort of relationship mood swings from external stressors, I’ve just learned to mostly ride them out without acting on them or vocalizing them. Mostly. I can tell my boyfriend I want to spend my life with him and things are calm and peachy, the next day I could be plotting my escape because he’s pushing all my buttons and I just want a break.
My personal theory is still that the constant barrage of stimuli that is daily life makes me more likely to become overloaded and need seclusion, and this could lead to apparent hot/cold relationship behavior.
Anyway. There’s no telling whether this is what’s up with your ex. Just a theory of mine.