You would get custody of your daughter if husband is agreeable in mutual consent divorce 

if he is not agreeable then you have to file petition seeking sole custody of daughter 

your extra marital affair is not ground to deny you custody 

- Yes, you can take his consent for mutual divorce , and which can be granted within a short period of time. 

- Your affair cannot be a ground for the refusal of custody of the daughter. 

- Under the Guardian and Ward Act, , the welfare of the child as the paramount importance, like ethical upbringing of the child, Safe-keeping of the child, Good education , and economic well-being of the guardian. 

- Further, as per the Supreme Court, for the custody of the minor, the only consideration is the welfare of the minor. 

- Under Hindu law, A mother usually gets custody of the minor child, under the age of 5 and fathers get custody of older boys, but it is not a strict rule and is primarily decided based on the child’s interests.

You can talk to him and make him agree for mutual consent divorce on the condition that the child custody will be with you and he can have visitation rights to visit the child periodically on agreed time and schedules.

The situation at his house is not conducive for the child's growth and you can very well argue upon the point namely he has a mentally retarded sister and old aged ,mother who cannot take care of her own self, hence considering the child's welfare is paramount, the child custody to be given to you.  

It further depends on how strongly you project your case in your favor.

Mutual Consent Divorce is possible even if counselling fails, both must agree to divorce terms, including child custody.

Custody of 5-year-old daughter usually favors the mother, especially if:

• You are financially independent.

• You can show a safer, stable home environment (vs unsafe conditions at in-laws’).

Infidelity alone does not disqualify you from getting custody — child’s welfare is most important, not parents' conduct.

Best way forward:

• Negotiate custody terms during mutual consent discussions itself.

• Mention clear parenting/visitation rights in the divorce petition.

• Highlight your financial stability, safer environment, and support from your mother.

Yes but custody has to be mutually agreed in consent terms between parties filed before court 

Dear Client,

1. 
   Mutual Consent Divorce: If counseling does not work, you may opt for a mutual consent divorce under Section 13B of the Hindu Marriage Act (or relevant law). You must mutually agree on matters like alimony, custody, and property. Courts normally grant it after a waiting period of 6-18 months.
2. Child Custody: Adultery alone will probably not decide custody—courts are most concerned about the child. With your secure income, the previous care of your daughter with your mother, and the dangerous in-law situation, you have a strong case. Documenting history (e.g., being physically injured by his sister) will make your case stronger.
3. Amicable Resolution: Limit harm, provide fair terms (e.g., shared visitation, no fault-blame). Try mediation. Don't resort to hostile actions—your daughter's needs and respect for each other can simplify the process.

Let the court decide issue as to custody of your child as your husband is not ready to accept only visitation rights 

If the case is going on in a court you may have to wait for the disposal.

You can strongly challenge the custody case if you find a good reason in this case 

Yes, you can get custody of your 5-year-old daughter through mutual consent divorce, especially if:

• You’re financially independent and stable.

• The child’s safety and well-being is better ensured with you.

• Your husband’s family environment is proven unsafe (e.g., incidents with his sister).

Infidelity is not a disqualification for custody. The court prioritizes child’s best interest, not marital faults.

Best Way Forward (Amicable Custody Plan):

1. Negotiate joint legal custody but physical custody (where the child lives) with you.

2. Offer liberal visitation rights:

   • Alternate weekends with father.

   • Mid-week video calls.

   • Shared holidays/summer breaks.

3. Include terms in the mutual consent petition itself to avoid future disputes.

Tips to Convince Him:

• Emphasize stability and daily routine for child.

• Highlight that he’ll still be involved through visitation.

• Mention that joint decision-making (education, health) will remain.

If he doesn’t agree only way is custody orders from court

Madam, 

It is hereby informed that in case of child custody case, the welfare of the child is of paramount consideration. Please try to convince and let him be sure that the child will be getting the best treatment of alround development in your custody and not his.