You tell her reality

You feel bad for Marta and tell her the truth,"I don't know what he is doing but he told me not to let you come home,"

Marta is suddenly shocked, "He is home? And why does he not want me to go there. I am going," she said as she got up,"don't worry I won't tell him you told me," and walked out. You try to stop her but unsuccessfully.

While you contemplate what you should do a few moments pass and you get a text from Sergio.

"What the hell man. I told you to keep her away. Fuck you man."

Turns out Sergio and Lucas were having a threesome with his GF and Marta caught him red handed.