Adultery The Cheating Wife ?

[RCF]

is Cheating on a Cheater considered as cheating?

Yes absolutely. One's own moral standing doesn't and shouldn't depend on others even if it means you are the victim else there will always be a murder for murder, theft for a theft and cheating for a cheat and no conclusion to it.
As for this story, if your ending is getting justice for Srinu then this would be a black mark but if your ending or plot is to make Srinu to understand his wife and her nature better and build a plot that cheating is not important for the couple but having fun is different than love and marriage then there is nothing wrong in the path he is going to understand temporary weaknesses.

~RCF