Panel 1: As he trudges to his Road Test Of Choking Like The Maple Leafs, Mike is aghast because the girl he never actually knew dared to break up with him. Since he's the same sort of imbecile Lizardbreath is, it can't occur to him that Martha felt that he already sort of did dump her but was too chicken to say so.
Panel 2: He proves that he has no idea how to treat a girl by thought-bubbling that Martha is the girl he took to Androgyny Night, the girl he wrote all of those "Enough about me, what do you think about me" letters to and the girl he gave a T-shirt to when she was expecting something actually romantic. If one were to try to explain to him that he deserved to get a crappy T-shirt as a sort of punishment, he'd get all defensive and yell "But that's different! I'm Mike Patterson!"
Panel 3: He feels hollow inside. He feels cheated. He's about to make people fucking hate him worse than they already do.
Panel 4: That's because he thought-bubbles he'd be the one breaking up with her....presumably after having caught her speaking politely to Jason Finkbeiner and thus validating his inability and refusal to trust anyone except for people who are bad for him.
Summary: Ladies and gentlemen, our hero! He actually wanted to catch Martha in a lie so HE could be the one making her feel bad! Her truth makes him feel bad because he was never able to ever prove her wrong. He's the one that's wrong and it sickens him. Not that he admits this. Her honesty is somehow a lie because it makes him feel like the victim.