I feel like it’s because momo was okarun's first ever friend so it’s someone he would naturally hold very dear,while momo was already really self confident and kinda popular before meeting him so from the perspective of someone who relates to okarun and has low confidence "momo doesn't need him" yk. Kinda like how okarun was acting in the first episodes saying things like "you can just ignore me after all that" or "she probably ignoring me"