(I could start it sooner, with Connor and Oliver on rocky ground, but Matt had no stones in that argument.) It starts when Connor becomes a demon, but unbeknownst to them, does not gain the means to eat souls. Following this, Connor begins to lose control and kills an innocent bystander, prompting him to call Matt to dispose of him. And well, at his own request, Matt kills Connor. The first thing he does is tell Oliver, Connor's boyfriend, about what he's done. It doesn't go well. But Matt tells everyone anyway. Wracked with guilt, Matt takes up Natasha's offer at drinks, where he shares his superhero origin story with her.
THE SAD TALE OF HOW KILL YOUR FRIENDS AND ALIENATE PEOPLE