It seems that according to the story, one breaks free from their ego and connects with the world when they discover the limits of their strength. Just like how Mon discovered that he was not god when he faced Higumadon and was killed, he returns the favor to Iijima in this chapter and kills him while reassuring him about his life decisions.
Iijima, who did not believe in human connections and society, could only find thrill when killing other living beings, yet deep down his conscience was disturbed. After he is defeated by Mon, he finally breaks free from the pit of nihilism in which he had fallen after the war, and says "I want to believe in this form of existence in front of me". He finally believes in something again. Thus, this was the form of "love" that Mon showed to Iijima, which was the same "love" the universe had showed him when he had his ego crushed in the earlier chapters.
