Caught in a Crossfire

Here's a situation for you little people. Play it out in your head.
It may require some flexible ethics depending on who you are.

Scenario:
You are out with two good friends. One of them is your significant other, the other, her/his best friend. Everyone's having a great time, until suddenly, a tiny issue is raised and everything goes sour.

Your significant other fires harsh words at their best friend. There is an awkward silence.

You are left alone.

Both parties are badly hurt. Your significant other is now emotional and regrets their actions.

Do you still comfort and support them?

What about the other friend? Remember, they're still a very good/close friend of yours.
Would it be biased if you tend to your own partner only? Will they feel neglected?

The best course of action is obviously to be Neutral. But what do you say to be neutral? How will you break the long silence? What do you do to mend the situation?

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I hope someone can give me an answer to this, because I suck at it. Thanks.

Send me your best answers, and you'll stand a chance to win a Sandwich... made by me.