I think it's beautiful that you want to be a good listener. You can still enact boundaries when the listening threatens to be painful for you.
Being friends with your children's father will be better for them. I have many friends that I wouldn't trust with my deepest secrets or with all of my heart. I know what to say and what not to say around them, usually. And if I say too much, I can pull back after.
With my H, I find it very hard to be friends with someone who is continuing to hurt me so much, I am only able to do it with a lot of prayer, daily, hourly, and to become very humble. I would not say we are friends when I am friendly, but I feel very free (from the slavery of bitterness/anger) when I am able to be friendly or kind. Tonight I even made him a cup of tea. He usually says no but he said okay when I offered, probably because he was out of money to buy wine. I was happy that he wasn't drinking and my daughter really enjoyed drinking tea with us and talking about her crush. It was kind of normal and no one thought about divorce while we drank tea. It doesn't mean that I don't expect him to be cruel to me again or to call off the divorce. It's just a little island in the storm before we set out again.
I believe I will see the bounty of the Lord in the land of the living. Wait for the Lord with courage. Be stouthearted, and wait for the Lord.