Ikkaku was reeling; his mind hadn't stopped twisting and turning in days, ever since Yumichika's betrayal. He still couldn't believe that the person who had been with him all this time, who had always stood at his side and watched his back, would end up stabbing him in said back. Had been lying to him, the whole time they were together. Ikkaku knew he wasn't really a thinker, that he was more the muscle in their relationship, but he still couldn't believe that he hadn't known, he hadn't suspected anything or seen any signs.
He felt dead inside. Even fighting couldn't make his heart feel alive anymore. Having Yumi there as a silent comforting presence behind him was something he had always taken for granted. He had always been there, and Ikkaku had assumed he always would be. He had believe, or rather assumed, that their partnership was perfect. He wasn't really a romantic, so he had never said these things out loud to Yumi, but he had always thought that Yumi felt that same.
Ikkaku also felt strangely disturbed by this new information. He was rather used to the idea of Yumi not being as much of a fighter, of him being weaker, and needing him. It hadn't exactly been a conscious thought, but still he had always felt that.
When he first found out about Yumi's zanpakuto his first thought hadn't been about that, rather it had just been shock and a deep feeling of betrayal. Not once, in all their time together had he considered the possibility of Yumi lying to him and hiding things from him. Yumichika was the one person he trusted completely, who he had always told everything to, kept nothing from. And realizing that it had all been a lie, that Yumi had been hiding his true power all along, made his chest hurt. He left it at that, sappy thoughts about broken hearts were for the weak, not something that happened to him, no he just experienced nearly unbearable chest pain.
After leaving the home he had shared with Yumi, which had been his first action after getting out from under Unohana's care. He had requested his own room, and removed some stuff from the small set of rooms that he had shared with Yumi ever since coming here. Picking through their belonging was a bit too much for him, even seeing their bedroom and bed was too much, so he just took the first things to come to hand, just some random clothes and his weapons.
But being on his own left too much time to think, something he wasn't really comfortable or good at doing. Since he was also under orders from Captain Unohana not to train, he had far too much time. He was temped to train anyway, just to stop thinking, but a deep set fear, um respect, of that woman held him back.
But thinking about Yumi was hard. And realizing the possibility that Yumi might be stronger than him, if he didn't hold back, was an uncomfortable and upsetting thought. Some part of him was impressed, to think that Yumi had come to be 5th seat in the strongest squad. Even while holding back and not using his full power. But a much larger part of him was furious that he hadn't told him. Sure, he disapproved of kido zanpakuto's, but Yumi was different. Honestly, once or twice when he gave thought to Yumi's powers and zanpakuto, he had been a little surprised that it wasn't some beautiful flashy kido zanpakuto, which would fit his personality better. Yumi was always so beautiful, and that his zanpakuto was so plain had always surprised him. So seeing Yumi's kido zanpakuto, all beautiful and sparkling, hadn't really surprised him on some level, he had just thought 'See, beautiful just like Yumi, how fitting.'
But how could Yumi not tell him? After all they had been through, after all this time together. How could he not trust him enough to tell him the truth? At the end of the day, that was what hurt, what kept him up at night, and kept circling around in his mind. That was where all the pain and anger originated. Not from Yumi having a kido zanpakuto, but that the one person he had trusted most hadn't trusted him. And he didn't know if he could ever forgive that.
Ikkaku knew he needed time to sort things out. He couldn't even look at Yumichika right now. For now, and maybe even forever, it was better he was not near Yumi. With this thought in mind Ikkaku decided that he should probably make arrangements for his current living situation to be more permanent. Which meant he had to go back home, to where he and Yumi had lived, to get the rest of his things. He knew that there was no getting around that, but also felt it would be best to time things so that there was no chance of running into Yumi. Facing the place they lived together was hard enough, he couldn't bear to face it with Yumi in it, he didn't know what he would end up doing.