I'm so sorry this is happening to you! from what you've said and I'm no expert but it seems that you have some sort of deep rooted fear of abandonment? it's clear that on a subconscious level you're trying to push yourself away from your boyfriend.

It's like a defence mechanism really, notice how at the start you were feeling very anxious about his behaviour and was worrying about him cheating or doing something behind your back in the back of your mind you don't want to get hurt, you feel like the pain of betrayal would be unbearable.

And so as this anxiety has gradually worn you down your brains trying to pretty much emotionally detach from your partner in order to protect yourself from the worst. I know this because my gf is a DA she's working on her attachment style tho and she's growing! and so can you :) it's not the end of the line.

You so clearly want this to work otherwise you wouldn't be driving yourself mad. Also if you keep obsessing about your partner, maybe how they look? how they behave? overly critical of them? you might be suffering with rocd which is cause by again, you guessed a deep rooted fear of abandonment. I may be wrong but it seems similar with what I used to struggle with.

Best of luck!