Welcome to the community, sorry you're here :-/
Wonderful questions; like all the best ones, not so easy to answer. If I were him, I'd be grateful to have a caring companion who wants to be helpful. That's huge, and don't underestimate the value of just being there say, when he injects. Right now, he seems embarrassed to treat in front of you, but for us T1s, BG tests, injections (pumping for me) and more BG testing is what normal means. It's what keeps us alive. Maybe (and I'm guessing) the best thing you can do right now is to just be in the same room when he tests, or injects. Not saying anything special, not doing anything special, just hanging. Being normal.
I doubt that was helpful, but I think in time you two will find that caring about each other goes a long way to working out what 'helpful' means.