What if I met a man and we fell in love. Then months later I find out that he is separated and working on a divorce. What should I do?

It depends where he is on the divorce. Like if he has been separated away from his wife for awhile and it is mutual I would say it would be okay. But if his separation is wishful thinking and she doesn't want it OR they are still living together or only separated for a short while and she hopes he comes back I would back off.

He was separated, so what, he was not living and had already left his wife. Divorces can take along time, some people don't push them.
If you love him, then he gets a divorce and you can marry

I would have a long talk with the guy and find out the entire truth about his so called divorce, how far along is it, is he living with her now, do they still have any intimacy. Then I would make a decision on what I would do. If the above questions don't suit you I would tell him to come back around after the divorce and you two will then decide which direction to go.

What if I met a man and we fell in love. Then months later I find out that he is separated and working on a divorce. What should I do?
Well I would be wondering why I was just now finding out he is married and if the separation happened before or after we met. It would tell me that he has been lying to me.
I would then start using my head instead of my heart with him.