I just finished this fun novel by Eric Luper called Seth Baumgartner's Love Manifesto. Seth is obviously the main character. His life takes a turn for the worse all in one day. It all starts when he visits his girlfriend during her break at the Applebee's where she works. She decides they need to break up because they've become "too comfortable" with each other. While there, Seth also sees his father and a lady, who is NOT his mother, cozying up in a booth. He hurries back to his job, only to be fired.
Most of the book focuses on Seth trying to get back with or get over his ex, finding a new job, and investigating this mystery woman his father is seeing. Of course, he gets in a lot of trouble on his way to figuring these things out.
Recommended for ages 13+