Do you ever catch yourself finding reasons, explanations, or even analysis as to why someone did or said something that was hurtful or harmful to you (or others)? Of course there are reasons for things. There's a reason for everything and when we care about a person or know a fuller history about them we can often find ourselves making sense of the mistreatment (towards us or others).
Doing that bypasses our own experience. It tends to move us away from our pain and being face to face with what comes next. You see, when we can reason or explain it away, nothing is really required of us next.
I am not saying to forget about or disregard their history, but rather see the complexity and still honor yourself. See their struggle and not accept mistreatment. Understand their pain without excusing them creating pain for you. Acknowledge their story without rationalizing their inappropriate behavior.