'Whatsername' is said to be the girlfriend of St-Jimmy/The Jesus Of Suburbia.
The character of St. Jimmy features prominently in the remainder of the album. His story continues as he meets and begins a relationship with "Whatsername", in the songs She's a Rebel and Extraordinary Girl. His strong feelings for Whatsername create a conflict within himself, between his new lifestyle and his responsibilities.
After getting close with Whatsername, there is an eventual breakup.In Letterbomb he is reminded of his duties to fight for the city. He then recounts his deeds and eventually disposes of the St. Jimmy persona in Homecoming.
"Nobody likes you, everyone left you, they're all out without you, having fun," is Whatsername taunting Jesus Of Suburbia, and writing him a goodbye letter. This motif later shows up in the end of the medley of "Homecoming." She explains that Jesus Of Suburbia doesn't care enough.
"The Jesus of Suburbia fell in love with Whatsername"