In "Beyond the Wall" (Game of Thrones, S07E06) ...
... when Jon was in trouble, Benjen Stark came and rescued him and helped Jon escape on his horse.
Why didn't Benjen tag along on the same horse and escape?
Why did he choose to fight the wights, which is almost suicidal?
I suppose this is the same horse with which Benjen Stark saved Bran and Meera in "Blood of My Blood" (S06E06).
So why not do the same here?