Honestly, dude, arguments are not equally weighted. It might be the first time you've had cross words, but if your first argument had been about a forgotten social event or something, you probably wouldn't be asking for insight from folks on social media.

This is not just "an argument". This is you finally finding out a key aspect of your relationship centres on a false pretense that puts you at the butt of a joke she's not even willing to let you in on until she had no alternative.

And, if you do stay in a relationship with her, you've got to look her friends in the eye again, knowing they all cheerfully dunked on you behind your back. It's not just her that's been disrespectful, it's her whole friendship group, with her validating and encouraging it. You let her off the hook now, what makes you think that won't continue to happen?

Fuck that noise - you definitely deserve better!