I think the issue of being friends with your ex is a lot clearer when there is infidelity. Let's focus on the classic WAS, who says ILYB. He/she has built a wall to shield themselves from the pain of the relationship which has also blocked out the intimacy/connection.
1. Can you be friends with this WAS?
2. Should you be friends with the WAS?
3. If not, should you make it clear that you will not be friends?
My WAW and I do not fight, are not hostile, and sleep in the same bed. We still enjoy each other's company despite the underlying tension and the elephant in the room. (She filed, but we are stuck together for the indefinite future because of the house and our inability to separate until we can sell it.) I think she is getting the impression that we will always be friends. I don't know that I can/want/should do that.