Your story is much like mine, and I think you are on the right track, by telling your wife how you feel and then giving her time to digest while you remain focused on her and on your growing family for a while. I told my husband about a year and a half ago about my feelings for a friend of ours, and that I did not intend to do anything about it. We have seen him off and on since then, sometimes as a family and sometimes just me, and my husband has grown used to the idea that my loving him hasn't taken anything away from our marriage, or threatened what my husband and I have between us, and he has developed a lot of trust in the other man.
Recently, I felt a lot more pain not being able to have a more full relationship with him, and with another man I fell for this spring, and I asked my husband to loosen the boundaries of our marriage. It wasn't out of the blue, since he already knew I had this in my nature. Things got ugly (you could follow my thread if you like) but then we came to a much better understanding of each other, and now he is fine with me being more involved with both men -just not sex or overnights, and he doesn't want to hear about it.
You have planted the seed in your wife's mind, and now by showing her for several months what a devoted, loving, supportive husband and father you are, if your heart still aches for A (or anyone) a year or so from now, it may be an easier conversation to have. I would hope you and A could have a casual friendship in the meantime, and that she and Z could get to know each other bit by bit.
I wish you the best!