Cheating is not the only "bad" thing anyone will experience in a commitment/relationship.
Indiferrence also makes a person feel emotionally abused. Though, everyone has their own preconception of what's good or bad, anyone would have a hard time controlling what would hurt them or not. It is a natural reaction.
Being in a relationship comes with being considerate to each other. But sometimes, I think, for every thoughtfulness someone gives to his/her SO, there is something which someone gives up on oneself.
I believe, this manga teaches us not to forget loving ourselves, at any point of our lives.
I hope the characters would find the contentment they long for.