Don't get too ahead of yourself. The very worst thing is expectations. You have expectations of something..and if those expectations aren't met, you'll be upset. The only way you'll feel good about it is if you have really low expectations and things work out well. I'd suggest that you consider that when she comes by that she may in fact ask for a divorce and tell you all the reasons why. She could be having an affair (yes, even if the "friend" is a woman...plenty of people haven't seen that one coming). Those are bad expectations.
I would steel myself to the very worst she could throw at you. I'd prepare a response to "I think we should divorce". Here's my example, "I understand that's what you feel is best. I don't want one, but if you feel that's the best thing for you then I wish you the best." Don't look heartbroken. Don't look beat down. Be strong. If it's an affair...don't know what to say exactly. Perhaps, "I see. Well I don't intend to live in an open marriage." Be calm.
With any luck, it's none of those and she just vents. Then you do the listening and validating thing. Got it?
You cannot be lonely if you like the person you're alone with. Dr. Wayne Dyer