You handled it really well. Your H was probably assuming you would get triggered and lash out, instead you stayed calm, admitted it was a little awkward, but that you were okay. It's not always wrong to share a little emotion here and there - you showed that you have emotions, you didn't overshare, and you can handle them. You even got feedback from your H that he was surprised! There will be times you get zero feedback, or even negative feedback. Enjoy the small victories!
Whatever your personal history aside, I think it's normal for your H to show increased interest in D4's life. It's going to be difficult to go through. I think you have the right mindset to focus on how it impacts D4.
