Would it be easier for you to ask him how he feels about you?

You seems to be thinking it through clearly and realistically. I agree you weathered each storm and came back from it to a baseline. I wonder what his feelings are- it is mysterious. Because of the ironclad rules, I don't think you will ever know, and the exact nature of his feelings will abide unspecified. However his actions speak more of a real affection then say my T's do toward me bc my T's music and his words go together whereas your T's music is quite personal, even though his words revert to professional when pushed. Your reasons for wanting to try out saying ILY seem very valid. It is a trust and vulnerability question- how much do you trust him, how vulnerable do you dare to be. . . The one thing for sure though is he is not going to buy that you mean you love him like you love your dogs. He will 100 take it as a full ILY.