What action to take against husband who has committed adultery?

We are Hindu married couple since 17 yrs. My husband had an extra marital affair since 2014. Despite of considering once, in 2017 I get to know that they are still in relationship. The lady is also married. I have sufficient audio proofs. I am asking for mutual consent divorce. But he is not accepting my terms on alumni. Our son is 11 yrs. He also wants a joint custody...or atleast a free access to child whenever he wants. Is it a good decission to approach court with adultery instead of trying to convince him for mutual consent? Please guide as I dont know what kind of time will go in court if i file a case against him.