You have to arrange that with the partner before the game begins.
Choose partner in bughouse

I see that you can lock onto a partner after you've played a game together, but is there a way to partner with someone before you've played with them? Or to go back and partner with someone once you've broken that bond.
Once a bond has been broken it is very difficult to restore. So we must cherish our bonds with other people when they still exist, and strengthen them so that they can last for years, and in rare cases possibly even a lifetime.

Salient point. But I'm still left wondering how I can pre-partner with someone of our mutual choosing and then try to be placed into a game. If anyone knows, other than to partner with someone you just partnered with randomly, that would be great.

@abstractactuary After you've chosen Bughouse, you should see something like "abstractactuary + Random Opponent >". Click on that and you can choose who you want to parter with.

If there are three other people that you know online, can you partner with one other and then select the other two to play against? That is to say, can one choose their opponents in bughouse?

I can't find the "partner" button when I click on my alt.
How do I partner now?
you shouldn't have an alt -_-
I see that you can lock onto a partner after you've played a game together, but is there a way to partner with someone before you've played with them? Or to go back and partner with someone once you've broken that bond.