@criver Abuse within a relationship does not an abusive relationship make. An abusive relationship has abuse as part of how those in it relate to each other, where it is normalised and blamed on the other.
Also she isn't psychotic, she's anxious and depressed. The only person she is at risk of stabbing is herself. You're conflating things. People with life-long mental health issues can and do have healthy, if sometimes stressful, relationships. The partner in that relationship has to accept the mental illness and act appropriately. A professional isn't always near, and neither always appropriate. Often it's just about minimising risk factors and maximising the more lucid moments. It can become abusive, most often self-abusive due to poor coping strategies, but it's not by necessity. Even schizophrenics can, when lucid, maintain normal romantic relationships so long as the partner is equipped with the understanding and coping ability to deal with when they're not.
Codependence is another issue entirely, and can happen between people without real mental health issues. There it is about enabling and emotional blackmail. Nothing if the sort is happening in this manga.