Wife going put with,receiving sms’s and cards from another man

Salaams, I have been married for 7 years, we had good times and bad times like normal marriages. After our 2nd child she starting gyming and lost lots of weight and is looking very beautfiful. This year my wife changed completly, she started going out late nights and not advising with whom she is going with. If I ask, she gets angry. She use to hide and talk on her cellphone. She use to get SMS’s and the name was a girls, only to find out recently that it was a guy all this time. I found love cards recently from this man. In my opinion I feel that she has been going out all the nights with this man. I currently seperated from her.
Mufti saab, please guide me what is the correct thing to do. I feel betrayed at the moment and am very angry. When questioned her about the cards, she kept quiet and has not given me an explanation to date.
i am worried as i have kids. Please guide me