As a practical manager, I would require that either Alice or Bob switch teams, far enough that they no longer need to interact, and also give either the option

As a practical manager, I would require that either Alice or Bob switch teams, far enough that they no longer need to interact, and also give either the option to amicably leave the company. There's not much more you can do. You address the tension, you don't assign blame, and you make sure both people have enough room to live healthy lives. Now, if this is the second or third time Bob has been put in this situation, he's gone. And if this is the second or third time that Alice has been put in this position, she's gone.