Which is "I won't be able to keep company to you for a while, but will you still be a good kid/behave?"
To which the character screams this reply:
I'm stumbled on the exact nuance of ことになってんだ in this. From context he seems... to be saying "How did it became that he's looking after me"? "Why did it become like he's looking after me?"
I assume the first bubble it's just a なんで but the actual nuance of ことになってんだ is what I'm not sure about.
I suppose it may ことになってる but it has various meanings so ?