Has your wife mentioned any complaints about your marriage, specific thinggs that bother her or needs that aren't met? If she were here telling the story, what would she say? You went to an individual counselor for your problems, were those problems related to her complaints? what specific improvements have you made?
Being a stay at home wife with 3 kids might not feel as exciting or fulfilling for her. You said you are best friends, so I'll bet you have a clue to her heart.
I would start there, but I would go dark. That isn't easy since you live in the same house. The problem is, you do not want to be cold or aloof. Is your work out of town or are you just working in an office m-th, and then working at home on friday?
I imagine in time, this affair is going to fall apart. Your improvements and care of your childrent and the interactions you will continue to have can help bring you closer together.
