Complex sentence: She begins to repent after she falls in love with Ryo and understands the hurtful feeling that she caused Momo, when Ryo seemingly gets her pregnant (it later turns out to be a medical condition that simulates pregnancy) and subsequently abandons her.
Split into simpler sentences: She begins to repent after she falls in love with Ryo. She understands the hurtful feeling that she caused Momo, especially when Ryo seemingly gets her pregnant (it later turns out to be a medical condition that simulates pregnancy) and subsequently abandons her.