They're both immature idiots that belong together. Hiromitsu deserves someone better and more mature for him. Adachi was also hopelessly caught in their extremely TOXIC cycle of love-hate. No relationship should be THIS complicated, it's just completely toxic and exhausting- which is why they bring up countless times how exhausting it is for the side characters involved. In the end this is the best for this shojo world to give everyone else around them a better life, since they are both so toxic to everything.