Something has happened and still happens in Wade's life. Whatever it is, it will most likely happen during the summer break. We can surmise it has to do with anal sex. This is over and above whatever is happening in the political world of his father and family. That part alone would be hell to deal with. Combined? Wade is broken, like so many of us.
So the guy (boyfriend) you're with goes off, at a party, and hooks up with a chick to conceal his sexuality. And we're surprised that the boyfriend hooks up with someone else?
Teenagers, hormones, uncontrollable emotions... Unless we're perfect, what else would we expect?
The real aspect of Matt that I see is that he needs some anger management counseling.