Finding Happiness In A Bad Relationship

Relationship work where we take responsibility for our feelings despite what the circumstances are seems very dismissive of what is actually going on. Choosing to find our own happiness and finding positive thoughts about partners that could be hurting us and betraying us in various ways (emotionally, physically) also seems like buffering in its own way. Choosing to replace negative thoughts in obviously bad situations in order to feel happy with ourselves feels dishonest about what is actually happening. How would one choose to end a relationship if we are always finding the thoughts that make us happy with this person? In trying to make this philosophy work, you could waste years of your life finding happy thoughts with someone who treats your poorly. Can you help me understand this? I see this question posed often in different ways in this forum and the answers always seem to be a couple of sentences about finding thoughts that make you happy in this relationship. I never feel quite satisfied with this answer.