Wife having extramarital affair

6 months into our marriage I came to know that my wife had a past and she is still pursuing it. She keeps lying to me and secretly meets and chats with her old BF(who happens to have a wife and 2 kids). Her BF wife is also aware of his affair but she is helpless as she is illiterate & dependent on him. I have asked my wife not to meet this guy but she always finds ways to meet him. My friends have seen them together (while she would lie about whereabouts) I called my in-laws told them all the facts and asked them to take her away till I decide. Looks like they were also aware of this affair but I don't have this confession in writing. I also shared with them interaction she keeps having with her BF(chats records about where/how to meet and phone calls logs). I am also disturbed by her attitude of behaving as a guest and not helping with ANY household activities, ignoring all my friends and family when they come over and showing no interest in this marriage when it comes to going out or having fun. I have now made up my mind to divorce her. How should I proceed? .