If Kirito knows that Asuna is fucking Inoda, but doesn't do anything about it, then this is not a cuckold, but rather just a slobber. In such an ending, Kirito has no motivation at all to stay close to Asuna.
There are many games where such behavior of the protagonist is explained by a desperate situation. For example, a job that he can't quit, and his boss is sleeping with his wife. Or the protagonist is in a club that he can't leave. Or he owes a lot of money, and the money is given by a neighbor who fucks the protagonist's wife.
And in the case of Kirito, there is nothing to hold him at all. Fujino is actually developing a rather strange scheme.
Kirito constantly gets hints about how good it is when another man fucks his wife.
Kirito succumbs to this fetish.
Kirito finds out that Asuna is fucked by Inoda and....what???
Is Kirito starting to enjoy it because he has such a fetish?? How coincidental it was! It's too simple and stupid. And if this is the ending, Fujino just leaves us with the realization that Kirito will now be watching Inoda and Asuna everywhere and be glad that they are fucking. It's better for Kirito to jump under the truck. Maybe "Go into a world where you have a whole harem of princesses, but everyone fucks them except you"
Sorry about that, just a thought.. If I don't say them, my head will explode.