Gaius showed his competence almost immediately, taking out another one of the unfortunate tools of their enemy, but then he dashed off on his own. Sirius hesitated, torn between staying with Harry and protecting Gaius.
"Stay together!" he called out. "Watch for the animator!"
After blasting another of the Inferi, he managed to fit in a glance at Gaius and realized that he couldn't return; he was protecting children. Sirius shifted to where he could keep an eye on his lover, and continued to fight.