What if you have to interact with the ex? How far do you go?

[AmsterdamAssassin]

I guess this mostly goes for divorced fathers or other custody cases, but how do you treat your ex-wife when you share custody of your children?
Do you interact often?
Do you only share about the children, or do you stay friends?
How do you have contact, calling / texting / chatting?
And do you shield your post-divorce private/sex life from your ex?

I'm not talking about the exes you want to keep in contact with, but the exes you need to stay in contact with, like co-parenting and shared custody.