I think you're gonna just have to bite the bullet and contact him, sure he may dodge it or not respond, but then you will know for sure that he either doesn't want to or isn't ready yet. You could even include a line to that effect 'hey, I know you're angry at me, I'd like to know why, but I know it's your choice as to whether or not to talk about it, but I'll be ready to listen to you if ever you do'. If he still avoids, then you will just have to leave him be until he is ready.In my initial post you can see that I texted him to let him know that he has become an uncle and his response was basically just congratulations. That's it! Like he doesn't care, and I know he does.
I had a thought - is there any reason why your brother may have needed to be paid back cash rather than taking a share of equity in a property? Not being paid back in cash may have left him in a problematic situation that he may not have been willing or able to talk about.