Make no mistake, they are both to blame in this relationship. Man, toxic relationships are hard, but the two of them knew very well that what they were doing was bad for the relationship. Even if you love someone, you know they cheat on you almost daily, yet you forgive every time, makes you just as bad in the relationship. It's hard to get out of, but Chikao has amazing friends who open his eyes, yet he is the one that continues to close them. At that point he's no longer a victim, he's victimizing himself.
Yuuji too, is just as bad. A typical example of a player. The worst of the worst. I imagine that the two of them won't be together anymore by the time they're in their forties. But the concept of the plot is quite realistic and I really like that. It doesn't have to be a happy story to be a good one. Sometimes protagonists of a story just suck and don't change for the better. Deal with it.
Overdose