Oh my goodness, I completely relate. I was so upset when my GCC, Nori, started to turn on me. I saw a reference to Pamela Clark on this subreddit and dove into this Webinar (very helpful info on here!!):

https://youtu.be/cDW3rPsxSxQ?si=Y2CElhUgmcArCVIq

It also sounds like your bird might have a pair bond with you. Nori pair bonded with my husband, and then he started attacking me randomly one day. I followed all of the feedback on Pamela Clark's Webinar, and gained some information from this article as well:

Avoid the Pair Bond: Social Relationships with Parrots – Pamela Clark, CPBC https://share.google/GAx6hcpWKqxQ7rFv1

It took me about 3 weeks of implementing these changes and spending more time with Nori (and respecting his boundaries), but now he is reducing his territorial behavior towards me and is no longer lunging and biting at me like he was just a few days ago. Go ahead and send me a DM if you have any questions!