The initial shock is always going to take time, take communication and then more time. When Kat talked to me about her wants, needs every negative thought that could go through my head did, every worst case became the most likely.
First up I wonder why you think you have outgrown one another? Obviously you love your wife, which in turn makes it obvious you want your relationship to continue.
For me the first thing to deal with was the sense that she must want to separate, it was, for me at least a natural conclusion to the suggestion that she wanted to see other people, sexually and emotionally. After much thought, a lot of conversation, a fair few arguments it became clear that you wouldn't argue over seeing other people if you didn't love one another.
Dust all I can say is take those negative feelings, write them down then pick one. For a day, a week, a month just think about where that's come from, why you feel it. I promise you these arrangements can work, and you won't believe this right now, but it can make your marriage stronger.
Chin up mate, it might look like storm clouds everywhere, but there is a sky above the rain.