Went way overboard with the heart ache but think about how this would affect the reveal that Matt's the man in the mask. Matt's feeling so damned betrayed after Foggy leaves, but he knows it can only be his fault, he should've said something, he should've asked Foggy if they were really together. It was so stupid to not question their relationship. If there's anything he's learned, it's that Stick really was right, soft things - as wonderful as they are - only hurt in the end.
And then on Foggy's side there's just so much confusion, because God, did he ever know Matt at all? And the reveal of Matt being the man in the mask and the reveal that Matt thought they were together get twisted up together. Foggy's pissed that Matt kept being a vigilante from him, and that unfortunately bleeds into his feelings about Matt thinking they were dating. He's just so mad he doesn't think, like what the fuck Matt, what's wrong with you? And he doesn't mean it, it just pops into his head. The problem is, Foggy walks away. He can't stay, he can't stand to look at Matt and know that he really never knew his best friend to begin with.
But Matt, Matt takes it as being completely rejected, once and for all. It drives in that idea that everyone's going to leave him. And this time it was all Matt's fault. If he hadn't been so stupid, maybe Foggy would've stayed.