Honey I had the same thing happen to me. Was with my high school sweetheart for 3 years. Suddenly his priorities changed. He was spending a lot more time with his friends when I had been his world before that. He started doing a lot of drugs like LSD. It’s like a switch flipped. I was devastated and I am ashamed even to this day of how desperate I acted. I pushed him away further. This has now been 39 years ago and I still hurt inside and miss him so much. I wonder if he thinks about me. We had just gotten engaged. J I have so many regrets on how I handled myself and devalued myself.
Don’t obsess over him. Don’t force him to have contact with you or go places that you know he will be. Love yourself and know that this is not about what you are not. This is about his illness. I know it still hurts.