His voice cracks a bit from the strain of keeping his attention on both the wasps and Jack and where he previously felt about as safe as he ever was fighting back to back with Angelus, he's now very exposed. He can't stay here. There's no reason for him to stay here.
"You're not trying to stop me from getting killed, you want me to lower my guard! That's what you do, isn't it? I'm not falling for that!"
He starts to back away, swatting at the wasps as he goes.