Last disclaimer: I don't own Phineas or ferb
Sunday
Phineas & Isabella were at a nightclub called "KOMET" and were listening to Streets (feat. Jack Evans)
Isabella: "Phineas?"
Phineas: "Yeah Isabella?"
Isabella: "I have to tell you something"
Phineas: "What is it?"
Isabella: "I have a big crush on you..."
Phineas: "I know"
Isabella: "And I've always been to ner... wait, what?"
Phineas: "I know"
Isabella: "And?"
Phineas: "I feel the exact same way"
Isabella: "Then how come you never said anything?"
At that point the song changed to Feelin' that way by (my favourite rapper) Adan Hicks
Phineas: "I never said anything because I was worried about what might happen, then when I decided 'never mind' and I was about to ask you out, you starter dating that S.O.B, Wesley"
Isabella: "Why were you worried about what might happen?"
Phineas: "What if we broke up fer a reason bad enough that we didn't even want to be friends anymore?"
Isabella: "At this point that's not possible"
Phineas: "Really?"
Isabella: "Yes"
Phineas: "Well in that case..."
Phineas then kisses Isabella (no tounge) and she just deepens the kiss. At that point they decided to officially become a couple.