Streets of Fire

In an unnamed city in a time period that resembles the 1950s (referred to within the film as 'another time, another place'), Ellen Aim (Diane Lane), lead singer of Ellen Aim and The Attackers, has returned home to give a concert. The Bombers, a biker gang, led by Raven Shaddock (Willem Dafoe), kidnap Ellen.
Witnessing this is Reva Cody (Deborah Van Valkenburgh), who hires her brother Tom (Michael ParÃ©), an ex-soldier and Ellen's ex-boyfriend, to rescue her. Tom returns and checks out the local tavern, the Blackhawk. He is annoyed by a tomboyish ex-soldier named McCoy (Amy Madigan), a mechanic who "could drive anything" and who is good with her fists. They leave the bar and later Tom hires McCoy to be his driver. That night, Tom and Reva plan to rescue Ellen; Reva contacts Billy Fish (Rick Moranis), Ellen's manager and current boyfriend.
While Reva and McCoy go to a diner to wait for Billy, Tom acquires a cache of weapons, including a pump action shotgun, a revolver, and a lever action rifle. Tom and Billy meet at the diner and Tom agrees to the rescue for $10,000, and that Billy goes with Tom back into "the Battery" to get Ellen.
In the Battery, they visit Torchie's, where Billy used to book bands. They wait until nightfall under an overpass, watching bikers come and go. Raven has Ellen tied up in an upstairs bedroom. As Tom, Billy, and McCoy approach, Tom directs Billy to get the car and be out front in fifteen minutes.
McCoy enters and is stopped by one of the "Bombers". McCoy, pretending to like him, follows him to his special "party room," close to where Raven is playing poker. McCoy knocks him out. Tom finds a window and, as a distraction, starts shooting the gas tanks on the gang's motorcycles; he then reaches Ellen's room, cuts her free and, with McCoy's help, escapes just as Billy arrives at the front door.
Riding in the convertible, Tom sends his crew off to meet at the Grant Street Overpass,and leaves to blow up the gas pumps outside a bar. Raven appears out of the flames and chaos to confront Tom. After learning who he is, Raven warns he will be back for Ellen and for him, too. Tom escapes on the one intact motorcycle. Billy is persuading Ellen the only reason her ex-boyfriend rescued her was for money. Tom returns as McCoy explains to Billy that Tom used to be Ellen's boyfriend.
Ellen follows Tom, while Billy and McCoy go back and forth once again about Tom and Ellen's love affair. Ellen and Tom also have an argument. When they all meet up on the street, they are in "the Battery". They return Ellen safely home where she initially rejects her home town as well as Tom. Later, he goes to the hotel where Ellen and Billy are staying to collect his reward. He only takes McCoy's cut and throws the rest in Billy's face. He then tells Ellen that there was a time he would've done anything for her but no more. As Tom storms out, Ellen follows and the two embrace in the rain.
Meanwhile, Raven informs Officer Ed Price (Lawson), the head of the police department, that he wants Tom to meet him alone. If he agrees he will leave the Richmond alone. Price tells Tom to get out of town. Tom, Ellen, and McCoy leave on a train. He knocks out Ellen and returns to town for a climactic fight with Raven. Tom defeats Raven and the defeated gang carries their leader away. Later that night, Tom says a final goodbye to Ellen and rides off with McCoy.

Question: What is Billy and McCoy going back and forth about?
Answer: Tom and Ellen's love affair