The worst part of being on the team for such a small amount of time is that Kouichi never had the chance to really bond with everyone. First, they were either suspicious or unsure of him, and at the time, he didn't blame them one bit. He couldn't see much beyond his self-loathing at the time, but he definitely saw that even though they said they didn't hate him or blame him or anything, Patamon was the only one who tried to befriend him. Patamon didn't interrogate him the way Kouji and Takuya did. Patamon actually tried to help him accept himself. And during that pivotal transition moment when he had to defy Cherubimon, he sometimes thinks it was Patamon more than it was Kouji who influenced his decision. Yes, Kouji's presence was a major factor, but Patamon had given him the hope in himself to be able to turn away from the dark.
Worse, when RhodoKnightmon explained the truth of his existence in the Digital World, Bokomon was the only one to talk to him about it. True, Bokomon, Neemon, and Patamon were the only witnesses to both of attacks that should have revealed his DigiCode but hadn't; but he still thinks that the others should have noticed it too. He knows that the only reason they knew there was something wrong with him was because Bokomon had to tell them, even if it was an edited version of the truth.
While he appreciates the help they were trying to give, he wishes they weren't so set on getting him to open up to Kouji. A lot of their attempts backfired in a way that only now can Kouichi see. In trying to encourage the brothers to interact more, they inadvertently alienated Kouichi. Rather than engaging him directly, they asked Kouji to speak with him. He couldn't go to Junpei or Izumi or Tomoki or Takuya for help—they pointed him in Kouji's direction, saying it was probably more right. They all forgot that even though they were working so hard to change that, Kouichi and Kouji were effectively strangers. Kouichi should have known just as much about the others as he did about Kouji, but he didn't. So when things came up that he had absolutely no way of telling Kouji about, he had absolutely no one else to turn to. And he is so glad that Bokomon of all people was the one to finally come over and ask him if he was going to be okay.
He doesn't hold it against them, but he wishes he was part of their inner circle. He doesn't want to feel like he's not one of them. He had Spirits just the same as they did and he fought Cherubimon and Lucemon just the same as they did. So maybe his experiences were a little (okay, a lot) different from theirs. It doesn't make him any less of a Legendary Warrior. And honestly, he's got stories they might want to hear. Sure, they can talk about the time they were all cooking and Kouji and Takuya gave each other food poisoning. Kouichi can tell them about the times he caught Ranamon pining over Mercuremon, only for her to realize that she had Duskmon for an audience. Even though Kouichi knows nothing about the cooking escapade and they don't know how far Ranamon's feelings for Mercuremon went (Kouichi isn't sure he knows either), but the stories are still good enough for them to laugh over despite it all. And that's all he wants, more than anything—to be part of this family. He just wonders if it'll be as hard to manage as fixing his blood family.