I'm so sorry for the untimely loss of your boa...that's hard, to lose such a young & seemingly healthy snake.

Unfortunately there's no way for us to know what caused this- the best information would come from having an experienced herp. vet do a necropsy to find out why he
died. You'd want to keep his body cool (in the refrigerator, but NOT the freezer) if you decide to do this...& you'll need to make some fast arrangements. It may or may
not give you exact answers, but it's nice to rule out some very serious & contagious ailments that might have caused this...especially if you plan to get another snake to
replace him...you want to be sure he doesn't catch the same illness from the pet you just lost. No way to know if there were any signs that you might have missed, like
is this your first snake? But you may have done absolutely nothing "wrong" & that would be reassuring to know also. How high were his branches? I suppose he could
have fallen & landed wrong, but that's not a common thing at all. Also, since he was so young, it's possible that he had some invisible defect that caused this, just like
some children are born with a "hole in their heart" that needs repair...that sort of thing can happen with snakes also, & they're so stoic! So, again...I hope you can get
some answers, but either way, so sorry for your loss.