Next step to divorce?

If she has got extra marital relationship after you married her, then go for divorce on the ground of cruety as well as adultery.  If you know him and if you can lay hands on some substantial evidence by engaging a private detective to prove her affair with that man, get that and also file a criminal case against that person, and this will create pressure on her and she will give divorce to you even on mutual consent.

If she is willing to have se x with that other man even after she comes back, and that includes  in her list of conditions, its advisable to file divorce based on adultery.  I really pity your situation.  Marriage works only on basis of trust and loyalty.  You have already caught her in the act and still want to get her back?  These kind of incidents look good only in tv serials and movies, not in real life.  If you have a brain, use it.  One could resolve the biggest of indifferences but not being unfaithful.

It will be murky, in court; if wife wishes to fight a divorce petition.  Its better to go for mutual consent divorce [MCD].  It'll be over even before you know it.  Dont pay her any money, just tell that you are letting her go without filing any cases against her.   If she does  not agree for MCD, then file divorce petition based on adultery and mental cruelty, make that person a party, get his address, get his 4 X 6 photo, hire a detective, start collecting evidences of your wife's adultery .

Thanks for the reply. 

Adv Chandrasekhar, in terms of evidence i have their mails which were exchanged and some face -book messages.. when i caught her she confessed she did lead him by writing all those obnoxious things and also confessed to me the same on whatsapp chat so yes i have a proof that she did have illicit relation... i don't think they got physical (well at least i assume) as he is married with 2 kids and stays with his wife in middle east. 

Dear Helping Hand.. you are absolutely right... this all looks good in serial... had she come back after this incidence and made some effort to make this marriage work it would have been fine and we could have resolved the internal issues... now its been quite a long time and she hasn't budged even after being caught i decided to move on in life and let enjoy with whom so ever she wants.. Also about 4 months back she accused me of drugging and all.. now i have my doubts that she is up to some thing.. and that incidence is very much engraved in my mind and heart... so its now impossible to accept her back in life... as you said being unfaithful is not acceptable on any level.. 

Only thing i pray for now is to get a MCD.