Infidelity

Hi Sir I am a working professional and was previously in a relationship with a associate in my firm. During the course of our relationship we had arguments and decided to take a break. We were working out and discussing our issues and I had gone so further as to propose marriage as per my partner's wishes. All the while, i was lead to believe that there was a future and she blocked my attempts to move on or change my company. One day it was brought to my notice by another colleague that he had seen her during an office party making out with a married man, who has two children. We had a huge argument and I found out from her watchman that the other man was visiting her since past 6 months and used to stay over till 11P.M almost everyday. Its a common gossip in my firm that they are together as they are seen everyday with each other and are never alone. I feel betrayed and have accosted her and we fought but she has denied the allegations. i have been considering telling the man's wife how her husband has been cheating on her with my ex-girlfriend. I haven't done it so far as she has threatened legal action saying i stalked her - when in fact it was the colleague(who now denies seeing them doing anything) and the watchman who gave me detailed account. My ex is notorious in my firm and many whisper about her promiscuous past and gossip. my question - if i decide to tell the wife of the guy or her brother what legal implications can it have? Realistically speaking, what would you advice me to do here?