Jamie and Cersei have a very spiritual twin bond. It is referred to a lot that they shared a womb and are each other's halves etc.

also, Cersei loved Robert a lot - A LOT, at first! But he was hung up on Lyanna and frequented brothels which made her resentful of him. Lannisters are about protecting themselves and Cersei takes that to the extreme of having her children be well.... Lannisters.


And actually to be more precise the REAL incestuous family are those Dragons, the Targaryens.