Rightly said by ld. memebers you need not have to proove anything infact if I would have been in your place I would have enjoyed the Court drama on how I forced myself upon my wife and it would be now wife's turn to take a long walk...........a husband has s*x with wife then also wife have problem and when does not have s*x then it is obvious that he is impotent so again a problem so let nature take its course wala hisab hai yaha........
See the point here is the more you accommodate a errant wife the more she will play "Arab and Camel" with you I hope you know the Arab and Camel story !
I would suggets you to invest on audio and video recording softwares and record all her "force foreplays" on such medias and produce them in Court like my old friend Purshotam from Mumbai did to get not only divorce but child custody form his wife. I posted his story somedays back so you take inspiration from such real life legal facts under such adversial henpecked conditions and evolve to be righteous human being.