Attend Samantha's wedding, after not telling her about Ryan's cheating, and choose to go to the bathroom. You will catch him cheating with Natalie. The day after the wedding, as long as you've got Samantha's lp up to 60 or more, go to the bakery in the mall and Sam will talk to you about how her marriage isn't going how she thought it would. The next day, after reaching 70 lp, she will call you and then ask to come over (she does this regardless of your answer). This will ultimately lead to her having sex with you and regardless of pregnancy outcome, she go take a shower and upon returning, you get the option of telling her you knew about Ryan. Do so and then choose to tell her she's wasn't any different. This results in an lp loss, HOWEVER it also starts alternate path D. The scene you're asking about is one of the last 2 on this route before the Ryan/Sam breakup.