My wife asked for a divorce a year ago. She flip-flopped from Feb '06 to Oct '06. We were in separate rooms as of July. She finally made up her mind in October, and she is FINALLY moving out at the e/o the month. Talk about difficult! And we have a 3 year old...
What did I do? I stopped talking about the relationship, supported her with the divorce, remained pleasant, tried to get on with my own things. It isn't easy, in fact it's the most difficult thing I've ever had to do. At times (especially lately) the tension is so high, it can make you physically ill.
The key thing to do is remain upbeat (even though you may be dying inside), don't argue, just agree and walk away, DON'T try to discuss the relationship, and give each other space. You can do it, hang in there!