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.)