Ferb

Yet another friend told him to 'try and figure it out'. Yet another friend made everything that much more cryptic. He buried his head in his hands and closed his eyes. After a while, he decided to sit up again and lay back on the couch but when he did, he was surprised to find his step-brother sitting next to him.
"Wow, you startled me" Phineas gasped.
Ferb just stared at him with an amused grin.
Phineas sighed. "I know what you're thinking. Why would I be sitting here, alone and sad."
Ferb gave him a stare which indicated that that was exactly what had been on his mind.
Phineas sighed again. "It's Isabella...She... said that she doesn't wanna be friends with me anymore."
Ferb's eyes widened in shock but he did his best to cover it up.
"I don't know what I did wrong, Ferb! I never wanted to hurt her... sure, there was that little miscalculation in our invention from last week but I said I was sorry and she even laughed..."
Ferb let his brother continue speaking while he formed a theory about Isabella's intentions.
"Megan said that you... that everybody knows why she's so sad... She also said that back with the domino course, she was happier than I thought and I have NO idea what that has to do with anything!" Phineas's screaming had gotten the attention of a few other guests who quickly returned to their own business again when they saw that it was chatterbox Phineas who was screaming.
Ferb on the other hand had made his conclusion. "Impressive" he thought to himself when he looked around the room for Megan. "Phineas... what am I to you?" he then asked.
"Uhm... what do.." Phineas started to say.
"Just answer the question."
"Well... you're one of my best friends of course."
"Wrong... I am your brother. Close brothers of course but brothers all the same."
"Okay... that then... but what has that got to do with..."
"And what is Candace to you?" Ferb interrupted again.
"Well, by that logic... she's my sister."
"Indeed. Now think of what mom and dad are to each-other."
Phineas began thinking about this one until he came with "they're each-other's lovers..."
"Try to figure it out, okay?" Ferb then said, forming a small smile on his face.
"Why does everybody keep saying that!" Phineas replied annoyed before going back to his thoughts. He started going over the list again. Buford's change of heart, Ginger's crush on Baljeet, Megan's happiness and Ferb's logic about their parents' love. Then suddenly, it struck him like lightning. His eyes widened in shock at the realization.
"Hey Ferb... I know what I'm gonna do tonight" Phineas then brought out with all of his determination. He then stood up, grabbed his glass of punch and started making his way to the garden again.
"Good luck, brother" Ferb told him.