i'm not sure you need to lovingly and sternly tell him "you really mean it, THIS time" do you?
he comes, he packs, he leaves. done!
here's the thing - he is free to TRY to come back at any time, regardless of what you say or how sternly you say it. you are not the boss of him. and he doesn't have to respect your boundaries or what you said on any given day.
The End is YOURS to uphold. if you are really done, then you are done. what he does won't matter. don't over complicate it.