He was torn between telling the truth and living his life. He felt guilty and horrible for tearing her from her mother...he knew it was wrong and even if it was Sugni's choice, he stood and let it happen. He feels he has done her wrong. However, he still wants to confess because of what has happened, so he asks her what she would do...what would be her reaction and it was more than what he could handle...She would kill herself. It is not that she would just leave him - she would die.
Knowing he could loose her altogether would be too much (I am sure she was being dramatic about literally killing herself)...even if she doesn't physically kill herself, he knews he will have killed her emotionally. She has, in heart, made him her husband and that's a big thing for a young Indian traditional girl. He can only assure her that his love for her is real; honor her by not touching her physically until they are married, keep the first wife hidden so she is going to be viewed as wife number 1...
But we all know the truth will be revealed on the wedding day and Sugni and TVS will break-up. What we do not know if they writers are still determined to do the Aditya Sugni jodi at this point.