Precise analysis
To add, Brett in that moment might've realized he can't love Hayden the way he wants to be loved, which made him even more hurt. Almost like Brett can't let go, but letting go would be the only way to love Hayden right. Hayden clocked that multiple times, mentioning stuff like feeling as if Brett wants to drop everything, from status to plotting, and just live, but is too afraid. I think losing control is what both have issues with, and what connects them so much as people. They might seem very different at first, but, as Brett kinda suggested at the beginning, they aren't so different from one another. They're different sides of the same coin.
I'd argue Hayden knows physical control while Brett is all about emotional control, and Hayden craves a way to let go physically due to his condition while Brett needs the emotional outlet. However, as of now, the relationship is only, to an extent, serving Hayden in letting go physically, but since Brett can't let himself feel, Hayden pays the prize for his limited freedom in a way. I think this will bite Brett in the ass (literally lol) and expose his own vulnerabilities in ways he won't be able to control. Like projectile vomiting - you hate feeling it, can't help it, it just happens, and it's provoked outside of your own control. I think that's what Hayden is to Brett regarding cracking the inner core
They are both cases of wanting control - Hayden by restricting himself and Brett by always gauging people’s intentions. It's interesting. Both are trying to protect themselves from the results of losing this control - Hayden with hurting people and Brett being hurt... That scene when it was revealed to Hayden that Brett didn't trust him, Brett was hurt because that was actually his way of showing affection. It was twisted but it was the only way he knew. Hence, he immediately cut ties with Hayden because he felt like Hayden wouldn't accept him for who he is. And, he would just make Hayden unhappy and he will not be happy when Hayden is not happy.
But now, I think he realizes that this is actually the lesson his father is teaching him. Different people, Different ways. If he wants them to be happy, he needs to know them, what makes them happy, and make compromises.