I’m so sorry you’re going through this, my STBX did the same to me in July.. much like you he had been loving and affectionate up until the moment he announced he no longer loved me.. he had even messaged me that morning saying “I love you so much my perfect wifey”... 12 hours later he had got in bed with me and told me he didn’t love me anymore.
If there’s any advice I can give it’s that you need to think about yourself, I spent months worrying about him and thinking he was having some kind of breakdown.. 7 months later and he has a new girlfriend who he is now renting a flat with .. I still find it hard to believe that he could do this to me.
You said Everyone thought we were the most solid couple they knew - Yup same with us, nobody could understand it.
You must think about yourself and do all you can to heal, seek counselling and reconnect with friends and lean on them and family for support.
7 months later and I don’t cry everyday, it still hurts and I don’t think I’ll ever properly get over it but I no longer lust for him to come back, try and limit contact as much as you can.. up until a few weeks ago my STBX would call me every few weeks in tears and then I found out he has introduced his new girlfriend to the family a day before calling me in tears.
Sadly the person you/I knew and loved no longer lives within inside them and there really is nothing you could have said or done to change this so please don’t blame yourself x