Keep the details someone shared in confidence out of arguments you want to win.

Using something told in confidence changes what the confidence was. The moment it appears in an argument, it stops being a thing shared and becomes a thing held, and the other person learns that everything they have ever said is potentially available for use. That door does not reopen. Winning the exchange costs you the version of the relationship where they told you anything.

Fight with material you gathered in the argument itself, and leave the rest alone. If something private is genuinely relevant, ask permission before bringing it in. When you notice the urge to reach for it, take that as a sign to stop talking for a minute.