"Be good,"
is something that people sometimes say
when they are saying good-bye.

I'm trying to be good.
Since missing you comes in waves,
I've secured a lifeboat
So I don't get swept away.
Instead of drowning in self-pity, I'm going to be good.

You didn't offer a good-bye.
You didn't offer any kind of sentiment such as "be good."
I might not be good yet, but I'm okay.