I personally would be checking with the landlord now. Because if you can't afford this place on your own, you'll be needing to find a new place. I know that in my roommate situations, if someone moved out, the lease was re-done, and if one person can't qualify for it on their own, OUT they go!
It was that situation (though a very calm "I can't afford this place that I almost FORCED you to move in to, so I'm moving out next month, sorry" sort of conversation, NOT an argument) that caused me to have my now-DH move in with me, which ALMOST led to the end of OUR relationship! (I wasn't ready to live with him, but wasn't willing to break my lease and get a bad rental history, and all of my friends and acquaintances had solid places to live)
So check now, to see if you'll be able to qualify on your own, or to get someone who can qualify lined up to move in if needed...(and be prepared to pay another background check fee), or to find a new place that you can afford on your own.
I mean really, I have had LOTS of roommates, and we had many arguments or testy conversations, but I NEVER wondered if a roomie was going to come back or not, based on ONE argument...sounds like this person was an interesting person to choose to live with!