Everyone goes into a divorce knowing what they want; no one comes out of a divorce getting all they wanted.
If you are unable to be flexible during negotiations you take the chance of walking away with far less than you could have negotiated.
He suddenly wanted to “just be friends” when he found out I had a child.
But what about the things you shouldn’t do during divorce?
If you are mad because he/she cheated and your goal is to make them pay, let that happen down the road.
Since divorce is governed by no-fault divorce laws, revenge isn't something you are going to get during settlement negotiations. Do Not Dismiss Your Ex’s Needs: You may no longer want to be married to him/her but that doesn’t mean you should ignore their needs. The legal idea behind a divorce is to dissolve a marriage, not leave the other person destitute. Plan ahead financially and start saving for the long-term.
In your case, a divorce would free him officially from his ex and allow him to start over with a clean slate.
So that begs the question: why would a man who has been separated for three years from the wife who cheated on him NOT want to divorce her? Which is why your question is better directed towards HIM than yours truly.