you can never "win" an argument with a liar. They lie. Period.
You can never have a reasonable discussion with someone who is unreasonable. They are unreasonable.
There is no point being honest with a dishonest person. They are dishonest. Remember?
Being nice to a mean person only helps the mean person. They take advantage of nice people. It is their way.
It is impossible to be more selfish than someone with a lifetime's of experience being selfish. They have the all the experience. It's uncomfortable for people like us.
No reason to beat yourself up. And every reason to change your mind. All you have to do is say you are uncomfortable with him there. End of discussion. When he presses you, and he will, politely remind him why he is going to court soon. Perhaps mention your legal team advises against him staying in the home. When he raises his voice, just pick up the phone and call 911 and report him. He'll leave. Trust me.
If he doesn't leave voluntarily and you won't call 911, go get a court order baring him from the place. What do YOU have to lose?