Wife Hid Her past before marriage

The fact that your wife had a physical relationship in past before marriage and the fact that such information was hidden from you at the time of your marriage vitiates your consent to such marriage. It can be assumed from your narration of facts, that such information was of material nature and had a material bearing on your consent to such marriage. Concealment of the same amounts to fraud and makes your marriage voidable in law.
Your marriage can be annulled at your instance. As per Section 12 of the Hindu Marriage Act, 1955, in cases where consent was obtained by fraud, the petition should be filed within one year after the fraud was discovered. Additionally, if the petitioner has willingly lived with the other party as husband or wife after the fraud was discovered, the court may not entertain the petition for nullity.

Alternatively, you can sit your wife down and talk about your intention to divorce her by mutual consent on account of the fact that you can't continue in this marriage anymore. You and your wife should agree to file a joint petition for divorce by mutual consent under Section 13B of the Hindu Marriage Act. That would take anywhere between 6 - 18 months (or even lesser) to conclude provided you have a settlement agreement in place with her covering all the aspects of child custody, maintenance, property division etc.

Seek the guidance of a qualified family lawyer who specializes in matrimonial cases and who will be able to guide you or counsel you through the legal process and help you understand the requirements specific to your case.