Is it OK to have affair with married woman?

Many married women engage in an extramarital affair if they suspect their husband is having one or have discovered the same. While having an affair with you, she may just be using you to teach her husband a lesson. Maybe, the great sex that you had was part of the beautiful revenge she had planned for her husband.

Is it a crime to fall in love with a married woman?

It would be a crime if a married woman stays in a live-in relationship with another person without ending her marriage. And the person living in such a relationship with a woman will be considered a criminal under Section 494/495 of the IPC.