You have two option:
1. Firstly, if your wife agrees, then you can file Mutual consent divorce under Section 13B of Hindu Marriage Act 1957. Further before filing MCD decide the terms and condition and also custody of child.
2. If she does not agree for MCD, then you can file divorce under Section 13 (1)(i) and Section 13(1)(i)(a) that is divorce on ground of adultery and cruelty. Further, it pertinent to mention that when it comes to adultery, the charge of adultery requires strict proof. While the courts acknowledge that adultery by its very nature is generally a secret act where direct evidence is almost impossible.
Madras High Court has observed that "It is unreasonable to expect direct evidence regarding such an act like adultery. It will be almost always committed behind closed doors and without witnesses. So, circumstantial evidence is all that can be normally forthcoming regarding adultery. The circumstantial evidence thus produced must however be convincing to the court which should be left in no reasonable doubt regarding the fact of adultery."
The Orissa High Court endorses this view of the Madras High Court by stating "To prove factum of adultery direct evidence is not necessary, it can be proved by oral documentary of circumstantial evidence from which the Court can draw inference beyond reasonable doubt that the opposite party had adulterous relationship with the third person."
The charge of adultery, in absence of any direct evidence, can be generally proved by producing presumptive evidence like:
(a) circumstantial evidence;
(b) evidence of non-access and birth of children;
(c) contracting venereal diseases and
(d) confessions and admissions
Indian law treats adultery as an offence under Section 497 of Indian Penal Code, punishable with imprisonment which can be extended for a period of 5 years. Section 497 of Indian Penal Code , 1860 reads as under:
"Whoever has sexual intercourse with a person who is and whom he knows or has reason to believe to be the wife of another man without the consent or connivance of that man, such sexual intercourse not amounting to the offence of rape, is guilty of the offence of adultery."
In view of above, you have an option to make a criminal complaint against the adulterer(the person with whom your wife is having affair) by invoking the penal section 497 and 499 of Indian Penal Code before the appropriate criminal court in India.
urthermore, with respect to custody of your child, your child is minor and that you need to file a petition for the custody of the children. Section 6 of The Hindu Minority and Guardianship Act states that the ‘natural guardian of a Hindu minor, in respect of the minor’s person as well as in respect of the minor’s property in the case of a boy or unmarried girl is the father, and after him, the mother, provided that the custody of a minor who has not completed the age of five years shall ordinarily be with the mother.
In your case, your child is 1 year old, so, in view of aforesaid section the Court will allow to retain the custody of your child.
However, incase you wish to retain the child custody, then you can proof the irresponsible behavior of your wife,so for appointment of declaration of any person as guardian, the court shall consider the welfare of minor. The welfare of the child is determined neither by the economic affluence nor a deep mental or emotional concern for the well being of the child.
The answer depends on the balancing of all these factors and determining what is best for the child’s total well being and thus there are numerous occasion wherein Supreme Court has allowed father to retain the custody of child.