Phineas is phasing in the backyard, looking at the ground. He's worried about what Ferb might think of him now. That was when the gate door opened.
Isabella: "Hey Phineas. What's wrong?"
Phineas looked up at Isabella, then knelt down.
Phineas: "Please forgive me Isabella, I didn't know you had feelings for me. I was just blinded by my adventures. Again I'm am sorry."
Isabella: "What- Oh. That's ok. Though, if I waited a little longer I might've given up."
Phineas: "Oh thank god."
Isabella took out a piece of paper and read it out loud, to Phineas.
Isabella (reading from the paper): "Phineas, you mean so fricken much to me. So if your body is ready, I would like to have sex with you."
Phineas thought for a moment.
Phineas: "Yeah. Yeah we can do that. Do ya... Do ya wanna do it right n-"
Isabella: "Yes!!! ... Sorry..."
Phineas took a deep breath. Took Isabella's hand. And finally, lead her inside. (And the rest, you can figure out.)
