Kisaki was having fun with friends, but his psyche was still fragile.
I don't think he truly "loved" ghosts, it is just that his power manifested as charisma to spirits and the skewed vision people had of him made him hyper-fixate on that "connection".
He respected Nimura-sensei very much and his wanting to leave the division to Makube must have looked like a betrayal, but sensei must have chosen that because he wanted to free Kisaki from that obsession and loneliness, if Kisaki simply stayed using the division as a crutch he would still be isolated from people.
And he chose Makube because he needed a more immediate reason to keep going... unfortunately, things must have happened in a way that he couldn't organize things like he wanted.
Now the question is if Nimura-sensei is alive or dead, with how things are with spirits, just his hand being severed isn't enough proof that he is dead, so he could be alive, but that still opens the question who or what is keeping him as he clearly was a very powerful practitioner.
I love Iruko's outfits, I love the double hair bun.