Their "attraction" happened when Victor was presumed dead and Chloe’s mother, Nancy told Brady that Chloe had died in a car crash. Chloe had been scarred and didn’t want Brady’s pity or him to see her like that so she made it seem like she died. Brady had stepped up in Titan and was living at the mansion with Nicole and was there to console him while trying to win him over for herself. That was when Nicole found out Chloe wasn’t dead and posed as a surgical nurse infecting Chloe with the flesh eating virus to keep her out of Brady’s life forever.
I’m just surprised that both Brady and Chloe have forgiven Nicole for what she did to them.