Even though slapping the wife comes under domestic violence under cruelty, the situation in which it was done by you should also be taken into consideration.  Which husband can tolerate the wife's illicit sexual activity with her boyfriend. Let your wife complain against you for slapping her under Domestic Violence Act. You don't worry since you have evidence of her illicit sexual relationship with her boyfriend. Based on the evidence the Court will take into consideration the circumstances which provoked you to act at that moment and it was not a domestic violence. You can try for custody of your child if his age is more than 5 years. Otherwise also you can try for joint custody/visitation rights.

In child custody cases welfare of the child alone is of paramount consideration.

Therefore, her adulterators life requires to be proved to cnvicne the court to get back custody of your child. 

How old is your child is ?

Well, single incidence does not counts in domestic violence but a case of hurt which is very minor in nature.

Abd if you have evidence of her adultery, you are at safe side even if she files any false case. So relax. 

Don`t give divorce but to teach her a lesson and intimidation, you may file divorce and later can withdraw it. 

Custody of child depends on his age and sole welfare of child. 

Court would consider fact that you found your wife had extra marital affair and so you slapped her 

2) you can seek joint custody of child 

It’s domestic violence only

1. Domestic violence case can be brought against you by your wife since you can not take law on your own hand and slap her.

2. However, since her act was very provocative, the Court might view it leniently.

Dear client, your wife can file a domestic violence case on yo for slapping her under sec 498A of ipc. You can use the evidence of video recording and can get divorce under sec. 13 of hindu marriage act under grounds of adultery. 

The defence which you can be taken is to be grave and sudden provocation i.e after knowing that your wife is in living-relationship with some one and after confronting her, you couldn't control and slapped her.

After the court granting the divorce you can claim custody of child.  And in recent karnataka highcourt's judgement if the divorce is on the grounds of the adultery then wife cannot claim maintenance from the husband.

- Since, you have evidences against her said acts of having extra-marital affairs , then her complaint will not maintainable 

- Further, if she files a complaint against you under the provision of domestic violence Act , then you can produce the proofs for her said acts 

- However, extra marital affairs is a ground of divorce , and on this ground she is not entitled to get maintenance from you. 

- As per law, the mother is the preferred custodial parent when the child is less than five years old. The opinion of a child who is over nine years old will be considered.

- However, to win sole physical and legal custody, you should show, the court that awarding you custody is in the best interests of your child due to factors such as your existing relationship with the child, her having extra affairs , and her inability to meet the child's needs.

The slapping incidence is the result of your anguish expressed over her behavior and illicit affairs, hence you can no doubt justify the same in trial proceedings if this matter is taken up before court. 

However if it is not possible to continue the marriage due to her affairs then you can file a divorce cae.

you can always get child custody by filing a child custody case under the provisions of guardians and wards act for the reasons stated by you including her illicit affairs 

whatever it is you should not have raised your hand

however it appears from your query that you had no intent to slap your wife

that happened due to strong emotions due to discovering the fact of your wife having physical relationship with another man

so the 'mens rea' or intention to commit any crime is lacking

she can possibly file for domestic violence, but you have a defense