Board Thread:FAQ Board/@comment-6697950-20160606184044/@comment-49.148.132.4-20160719090632

I've observed that their relationship is one of the established immutable things in SAO, whether in the LN or WN. And while Asuna will never delve as deep into the VR world as Kirito, she's basically his anchor to the real world and he knows it. All the other girls do have feelings for him to one extent or another, but they do observe the limits of the territory since they all acknowledge that Kirito is spoken for already (Lisbeth and Suguha are perhaps the most aware of how deep their bond runs).

Them 'breaking up' is just a mechanism in the games (which are non-canon) which basically allows you to move around with more freedom while still being Kirito.