When it comes down to it, I think he's a pretty selfish person who has demonstrated that he's mostly concerned only about himself. I feel like he has treated Yo Yo pretty poorly. Yo Yo got her arms cut off by Ruby, and Mack didn't seem to have enough compassion for her, to the point when she killed Ruby to stop her from turning into the Destroyer of Worlds (and partly out of revenge), he got really really angry with her. Then when he became Director, he dumped her. And promptly got jealous when she got together with a new agent.
Above all, his actions this season have been appalling and hypocritical. He chews out Deke for killing Freddy Malick. But has no qualms jeopardizing the entire mission because he wanted to save his "parents". His actions led to the direct exposure of the team and compromised the mission. His parents turned out to be Chronicoms. He was in mourning for them but instead of recognizing that his friend is there for him, he pushes Deke away. For 20 months, Deke has been trying, and he has financially helped out 10 year old Mack, his brother, and his uncle.
Mack is just a selfish and ungrateful ass. He doesn't deserve any of them, but especially not Deke.