Well, what do you know... Even Buford has it in him... well, at least he did once. Here's the deal. In the Phineas and Ferb episode "Buford Confidential", three Fireside Girls from France make their appearances and Buford recognizes the one named Brigitte as his former lover back when he went to Paris himself a year ago. The two fell in love and Buford learned to speak fluent French for her. Now this explains how he was able to do so in "Summer Belongs To You" and it also explains him saying, "Love is a canvas furnished by nature and embroidered by the imagination" and why he says that Paris does it to him every time, as if he had visited Paris once before. But something had to happen. Something had to have gone wrong somewhere. Because it is stated that the two of them are not lovers anymore, and I mean besides that they live in separate countries. Then again, Buford had become a bully years ago, so that could be a factor, except that he only really bullies nerds and Baljeet is his numero uno. So what really happened? Find out in "Buford Confidential", assuming it has the answers.
There, you see? Whether things fall out or not, if scenes like these can happen, adding on that Buford was a year younger by technicality, why in the hell do we still not see any advances in Phineas and Isabella's relationship? Their time in Paris was a complete blowout compared to Buford's, so this would probably be grounds to make 'Phinbella' fans cry. Because at least Buford had charm while Phineas currently has zilch, technically, and is only attracted to things that aren't even cute at all. To be blunt, Phineas and Isabella's relationship has been one-sided for too long. Next thing you know, we're gonna hear of Ferb having a secret girlfriend or something, leaving Phineas last on the line. Typical and ironic.