Carly's husband. You act as if she has mind control or something. Sonny got his memory back and he retained his SMike memories--which included his love for Nina. Sonny is the one who insisted that Carly and his family leave Nina alone. Sonny is the one who testified that he didn't want Nina to be punished.
Carly chose not to show up to Sonny's romantic rendezvous. He then turned to Nina 100%. He made a choice between the two women. I am not talking about NF. I mean once he got home. He was still married. He was living with his wife. He was in love with two women. He made a choice of his own free will.
Carly continues to be the victor. So yes, Nina is the underdog by definition.