Not that I know of... If Incest wasn’t a big deal, Cersi and Jamie wouldn’t have been willing to toss Brant so casually from the tower just to keep their secret....
Incest is not something that the GOT Universe has ever embraced as acceptable, even though its been part of the story almost from the start.
The fact she found out her lover was her nephew didn’t even seem to register, simply the fact he could be a competitor for the throne...
“...The fact she found out her lover was her nephew didn’t even seem to register, simply the fact he could be a competitor for the throne... “
That was my interpretation of that scene also!
Incest is frowned upon in Westeros (except for the Targaryens), but the primary reason Cersei and Jaime had to keep their sexual relationship a secret was because Cersei was married to the King. For her to have sex with someone other than Robert was considered treason - for her and Jamime. The reason for this was because she had to produce legitimate heirs for King Robert.