Section 12(c) of the Hindu Marriage Act states that a marriage is voidable if the consent of one party is obtained by force or fraud. Fraud must affect marriage fundamentally. In your case, it doesn’t affect the marriage fundamentally. Affair before marriage and its non-disclosure at the time of marriage cannot be a ground for nullity.
The scope of word fraud is limited to these purposes:
- The nature of the ceremony or
- Any material fact or circumstance concerning the respondent
You can file for divorce on the ground of s*xual intercourse with another person under section 13(i) of HMA, 1995. If you have good evidence of s*xual affair after marriage, it can be granted in about 18-24 months.
Hope this helps!