Yeah but there's also the thing with his family (from chapter 32): he clearly feels inadequate when he's around them, and Urumin is almost like a lifebuoy or a beacon of light to him, so he's been desperately latching onto her. She isn't the only one keeping him afloat (there's also Kuzutani), but she definitely plays a big part in him not acting and feeling like a complete mess with no reason to live anymore.
To me, the "who am I here for?" felt not like Kimiya beeing angry at Urumin, but like him losing his light and the only thing that made him feel like he mattered to anyone. ...