Isabella

Phineas made his way back to the garden through the living-room where Megan gave him the thumbs up and where Baljeet and Ginger smiled at him. He passed through the garden again where Buford and Adyson wished him luck. Even though Phineas did not reply to all this, they didn't mind since they knew Phineas had something more important on his mind.
Isabella had seated herself on a small bench at the side of the house. It was still in Megan's garden, only it wasn't visible from the living-room or even from where Buford and Adyson were. She wondered to herself whether she had made the right choice until suddenly, her crush stood next to her with his glass of punch clutched in his hands and a determined look on his face. Though it was full of determination, it was also full of guilt. Guilt that he was now going to redeem.
He sat himself next to her, held up his glass and urged her to do the same with her glass. All the while, no-one had spoken. Isabella, though confused about the red-head's intentions, raised her glass, curious about this move.
"To our love..." Phineas then said.
Isabella's eyes widened and a smile slowly crept on her face. After all these years, Phineas had finally found out! "To our love..." Isabella managed to reply and soon, their glasses touched.
Phineas then took a small sip from his drink while Isabella just stared from him to her drink. Finally, she decided to just toss it aside and fling herself around his neck. "Oh Phineas!"
Phineas was quite startled by the move but it was to be expected of course. After all, Isabella has been waiting for this moment for a long time. Maybe even since the day they met. When he gathered himself together again, he placed his arms around her waist, hugging her tightly. "I'm so sorry Isabella... I should have known that..."
Isabella interrupted him. "Yes, you should have... but... you did now..." Of course she wished that it happened earlier but she was too happy right now to worry about that. Her patience was rewarded at last.
Phineas, on the other hand, still felt incredibly guilty for making Isabella wait all this time. He knew he liked her more than anyone (except for Ferb perhaps) but it all clicked when Ferb started about love. He tried and figured it out. He now knew why he felt so connected to her and the realization was enough to make him feel good as well.
The two broke apart for a moment again, just staring into each-other's eyes. Both grinned at each-other, making the other one blush and grin even more.
"I... just hope Megan doesn't see this. It's her house and she knows what's going on" Phineas whispered with a chuckle.
Isabella gave him a confused look and wanted to ask what he meant when she was embraced in a kiss. Her eyes widened in shock but soon, they closed.
The couple, which was bound to happen ever since they met, kissed at last.