You don't need me to tell you that breakups suck, which is why I'm here to tell you that breaking up when you live together is so. much. worse. Do you continue living together like Nick and Jess did on New Girl? God, I hope not. If you go your separate ways, who gets the apartment? More importantly, who gets the dog? It's a logistical nightmare.
Plus, there's all the legal and financial issues you'll face if both of your names are on the lease. A friend of mine recently got stuck with a $2,000 early move-out penalty because she broke up with her live-in partner and they wanted out of their apartment. Unbeknownst to her, the charge went unpaid for years until she got married and tried to rent another apartment with her husband. Imagine having to track down your ex years after a messy breakup to ask them about a mysterious debt from long ago. He replied that he'd already moved on with his life and that he didn't necessarily need the charge removed from his credit history right now. Um, OK, bro. She covered it all on her own.
Emotionally, breaking up with someone you live with is just as taxing. I remember when my last relationship ended. I got the apartment, but that meant I felt overwhelmingly guilty about ~kicking my partner out~. To make matters more complicated, he disappeared for a while after our breakup, leaving me to coordinate move-out times and logistics with his mom. I tearfully packed up all of his stuff in a few hours. She arrived (with a support system in tow and three separate vehicles) at our scheduled meeting time and didn't say a word to me the entire afternoon.
I guess you could say I know a thing or two about the brutally honest phases of breaking up when you already live together. In my experience, there are three of them.