Eric Bernie's Transactional Analysis (TA) which is used in psychotherapy etc. extensively deals with three ego states of mind - Parent, Adult and Child, all within the same person. Without getting deeper into TA, let me tell you that even when the Adult ego state brings in rationality, the Child ego state can become irrational and neglect the rational, logical approach of the Adult. In what you are explaining as your state of mind right now, I tend to find this situation. You are in a relationship with a person who is undergoing treatment for mental health issues. You are getting signals of the relationship being uncomfortable. You are also getting caution from your Adult (going by TA) about the inconsistencies in it. Yet the Child within ignores them and clings on. This is not at all unusual, especially when it comes to close, romantic relationships. Yet we need to be logical and rational before making any decision that is going to be lasting for a lifetime. With all these, I feel you need to consult a psychologist to help you in your decision-making.
Next Steps
Please consult a psychologist.