Ah yes, the much vilified ex-boyfriend character. Porter is the boy who didn't quite break Frankie's heart, but her certainly bruised it. At first, we see him as a fairly two-dimensional character; he's just some jerk who cheated on Frankie and is in the Spy Club of all things. But soon, he proves himself to be rather multifaceted. Frankie finds out that he's next in line to be the Basset King in the same secret society that Matthew's in.
And in the end, it turns out that he's the one who was spying on the Loyal Order of the Basset Hounds all along. Dude's a double agent. When Frankie asks him why he did it, he responds with the following:
"The last thing I want is to be like my dad, Frankie." Porter shook his head. "Or my brother. You should remember that. I hate everything they stand for." (44.53)
At the end of the day, Porter and Frankie still have something in common. They're both pushing against the constructs that box them in. Both are tired of the Old Boys' network and how it operates, even though their dads are both very involved in it. They're trying to differentiate themselves by taking down the institution that they were always told to respect, for no concrete reasons.