Snapped: Killer Couples (2013)

S4E47 Act Your Age

A decade has passed since the last adventure, and Phineas faces the big decision of choosing a university. Just as he learns that Isabella has harbored feelings for him all these years, he realizes he must find her before she heads off to college and confess his own feelings. At the same time, Doofenshmirtz is grappling with a mid-life crisis, adding to the chaos of this pivotal moment in their lives.