Leo does as he’s told without question. He trusts that Donnie is ready, if he’s telling Leo to drop it.

He may have gotten hurt, but he’s jumping back in there. Leo is proud of him, even if he feels a little worried, too.

But as a sibling he also can’t show too much concern or Donnie might think Leo thinks he’s fragile. So he drops the portal and ducks out of the way to let Donnie do his thing.