Oh, you poor man. I think poor Richie's heart was broken when Carmy left him behind.
"I didn't realize how you lost someone too" is not Carmy realizing Richie lost Mikey. It's Carmy realizing Richie lost Carmy.
I think it hurt Richie so much and Carmy had no real idea that of what they had meant to each other and what they had lost because he had been the lost child and was so fixated on Mikey.
Mikey destroyed himself but to do that successfully he had to take Richie's son away from him first. He could manipulate Richie. He could not beat Richie and Carmy together, and he frankly could not bear the notion of being left behind to his insanity while they teamed up without him. I don't think Carmy and Richie were "allowed" to evidence loyalty to each other in the presence of Mikey. You can kind of see this in "Fishes." They probably were only semi-conscious of it but part of pleasing the charming tyrant was centering him.
So they just focused on Mikey and used him as a shield of sorts. He was their beard, but the secret relationship that never got named was brother/cousin/father/son/etc.
I think Richie raised Carmy. He touches that kid and Carmy comes back to earth. He can reach the inner Carmy while the outer one has short-circuited. "Don't fuckin touch me" we hear from Carmy to Mikey. But we see Richie and Mikey repeatedly touch each other to reconnect and check in.
I think Mikey would have liked to have been Carmy's replacement dad, but I think he was very dangerously unwell, and he kept away, and just told cool stories to fill airtime. The moment in the pantry when he was open and vulnerable was the exception. The rule was "never stop talking and yelling and fighting and drinking or you might cry and they can't see that."
I have no doubt Mikey adored his weird little angel baby mute puppy brother but he couldn't and wouldn't let him close. It was physically, not to mention emotionally and behaviorally, dangerous for the little guy to be near Mikey, and Mikey knew it.
So Richie did all the work, and listened, and tried to teach the kid to read (hard) and do math (very hard), and was really really in love with him and proud of him, and Carmy took him for granted and yearned for Mikey because he knew he was never getting anything from his bio-dad and his much older bio-brother was the next best thing.
And that was kind of OK with Richie, because helping Carmy was a way he could stay "useful" to Mikey and Donna, and then maybe they would love him and let him stay. Richie's access to Carmy was predicated on their approval of him; they were the gatekeepers. He was like a hired babysitter in a sense but the currency was love and codependency.
"Yeah but you knew him. I didn't really know him."
Mikey started mentally declining so he sent Carmy away. Shunned him.
I am almost positive that Mikey lied through his teeth to Richie about Carmy. We will see more in season 5, but I think Mikey isolated himself so he could kill himself in peace, and to do that he had to fracture the family, and pit Richie against Carmy, visa versa, and kick Carmy out wholesale because Richie would never leave and for that matter did not have the resources to leave, and neither of them understood what was happening, and they resented each other instead of laying the blame where it rightly belonged: at Mikey's feet.
Sorry. I know Mikey is supposed to be the secret hero but he abandoned his child even when he was alive and Richie stayed and did the work.
"This is my home. I'm not going anywhere."
