If she has affair with any one else, you can directly talk with her and may proceed for mutual consent divorce. In case she has affair, she will not oppose your proposal for mutual consent divorce.
In case you need contested divorce, denial of s*x is no ground. This becomes ground by trating the same as mental cruelty. But, as you know proving same is difficult. Only in case she is virgin and medical confirms the same, you can either explain it to be denial of s*x or to be impotent if not physically then at least mentally as being not ready to s*x, which is common. Either way its all interpretation of same thing in different ways, which your advocate may argue better.