You aren't alone! I'm in my 40's too and had what was called "elective mutism" back in the day. It started with adults I didn't trust then it got worse and I barely spoke to my parents and other kids my age. That problem went away with a school change but I was still shy.

I have had a lot of good therapy and it does help. I still have anxiety issues but I'm working on it. I've seen others on PC with selective mutism in their past. It isn't a joke. I hope you can get someone to educate your boyfriend a bit more.