Most Helpful Guy
Whoever can afford to live there by themselves or if both names are on the lease, whoever pays the most including other expenses , now if expenses are split 50/50, then maybe decide by convenience like for example, is the apartment more close to your job or your SO's job kind o thing.
Most Helpful Girl
Whoever's names it's in. In our situation, we're both on the lease and I would be the one to move out. His brother lives with us so it'd make little sense for me and his brother to live together and him to move out or for me to live here and both of them move out. It'd be most convenient for me to move out and them two to stay here.