I got news, my friend, this happened to my fiancée and me when we had a kid, but luckily resolved when I helped her with, pretty much, all house chores. However, much later we went into a similar downward spiral only this time the culprit was work. I'm currently trying to revive our passion from when we first met, and it's hard. We're only in our early thirties (we met at 18) and our sex life is average, but our relationship is strong, albeit the lack of communication and loss of interest in sex. However, this is not about me but you.
It concerns me to hear that your wife doesn't care if you get sex elsewhere for three reasons:
(1) Either she doesn't feel sexually attracted to you anymore;
(2) Or is too tired to have sex or lost libido (sometimes it's due to illness);
(3) I will not mention the third because I suspect your wife loves you.
However, personally, just like me, I suspect your couple to suffer from lack of some "alone time," which some member on this site reminded me. If you two can get some time off together and rediscover your love then kudos to you (it's not the case for me), and this could help bring fire back and passion into your relationship.
I hope your couple works out because you have a long history together and I surely hope mine does as well. I love my wife, and so does she, but sometimes the fire burns low, and it is up to each partner to work together to relight it back into a blaze.