When a poly family splits, usually like in a any split, hurt feelings exist. It's important to NEVER defame, belittle or put down any of our former partners to any one. We should always speak kindly of them or not speak about them at all. It reminds me of an old saying, "If you can't say anything nice, then say nothing at all."
I know at times this can be difficult. We may feel the need to defend ourselves if our former parnter is talking badly about us. Remember though, when others say bad things about us, it says more about them than it does us. We do not need to defend ourselves to others, nor is it really any one else's business as to why a split occurred. We do NOT need to air out our dirty laundry to others, nor do we need to air out the dirty laundry of our former partners. To do so is a vindictive, childish act only meant to harm someone we once loved or may even still love.
Let it go and move on! This is the healthy thing to do.