James | McGonagall
Look, this is the most rational decision Sirius has made in a long time, his club aside.
And even if it wasn't, they're both consenting adults and we can't stop them from making a mistake. All I can do is be there to support him, and help however I can.
I know your support means the world to him, but with all respect Professor, we're not your students anymore. This was Sirius' decision, and he's going to see it through to whatever conclusion it comes to. If he's very lucky, it will work out. I hope it does.