I'm sorry you two aren't in touch anymore, especially since you felt so safe with him in your life. Are you able to figure out what about him made you feel safe, or if he reminded you of anyone who might have been your safe person growing up? that might help you to understand why you felt that way around him, versus other people.
I have had times in my life where a lot of the cross talk goes away and I don't seem to need to switch. I also struggle with wondering if it is me being 'all-in' or if it is a part that is separate from the others. I do have one part that doesn't hear any of the others, and when I switch to her I tend not to have many issues because she also doesn't feel fear and vulnerability. However I also get physically sick from stress when she's out because the others are still there feeling upset, she's just not dealing with it, so it turns to physical symptoms of stress.
What you talk about sounds different than that, and more how I was feeling at a certain time in my life when I was working/studying, and had what felt like a full and happy life. It wasn't because of a specific person in my life, but I do attribute it to being busy, happy and the town I was living in at the time.
So, I dont' have any answers for you, not that you expected any. Just thought I'd send a message to let you know you aren't the only one, and that you're not alone in the wondering. I might bring that up with my t at some point and see what he has to say about it, actually
xoxo
IJ