Husband Confused about Cheating Wife

Hello, here I am going to narrate a small incident, how my wife cheated me. Now we are Confused what to do! The incident that I am going to tell, happened on 21st may 2012. Few days before of which I and my wife had series of fight due to silly matters. My wife is 31yrs old, fair looking and we enjoy very good sex life.
We have 2kids and She was very sincere Till this incident happened. She went to her native for about 15 days for a change. Her maternal uncle’s son by name chetty, who is 2 or 3yrs younger to her, came to know about our fight and tried to get close to her. After She came back home, we were normal. Few days Later one fine day, chetty came to the town where we live.
My wife asked him to come by noon as She was yet to complete her household work. He later has come along with some hot drinks bottle and soda. My wife had little interest even to have hot drinks. He was talking to her very nicely, appreciating her beauty and he gave her the drinks. After having it my wife got good effect of the same and was enjoying it.
He slowly went close to her and started touching her which She at first opposed. Later he went and closed the main door. He then went to bedroom and called my wife to switch on the cooler. When She went in, he grabbed her, hugged and started kissing her. The effect of the drinks and little reluctance about me made her to surrender herself to him.
He just lifted her nighty, made her to Sleep on bed, removed his pant and underwear very fast. He fucked her very fast while my wife was under the effect of alcohol. She was not in a position to resist or enjoy the sex fully. But the mistake was over. She realised it little later and asked him to go as soon as possible. He had lunch and went away.
She tried to behave normal with me after I returned that evening from office. I just happened to see her mobile and asked her why has deleted her call list. She told She wanted to avoid getting doubts in my mind. So She deleted frequently called number and thats is of her cousin, chetty. Till then I never had got any doubts on her.
But, Next morning while I started to my office I smelt something fishy. I came back home and asked her to tell, if She was hiding something from me. After a lot of questioning She started crying and revealed everything that I narrated above. I dont know from where I got so much of patience, I consoled her telling that mistake happens. Please dont repeat it.
Later She called him over his mobile in front of me and scolděd chetty for having trapped her. He too said sorry and promised that he wont repeat it. But She dint tell him that I know the whole incident. But next day She told that he made call to her once again. I got angry on him and I shoúted at him over phone not to disturb once again.
He was shocked by my words and now avoids both of us. But now a days my wife revealed that She wants to keep in touch with him. I felt She too love him and may be want him back. One night while having sex with me, She revealed that She wants both me and chetty. I felt I have to satisfy her physical need.
Even I had read a lot of threesome sex in HD, and other blogs, I asked her whether She wants it. She said NO. She is very happy about sex with me. She dont want sex with him, but She want to keep in touch with him as a friend. Now I am Confused as to what really is in her mind?
She Later oneday called on his mobile and spoke for a long time where he expressed that he does not want to keep in touch with her. He too is married and have a kid. Now my wife is feeling that She was used like a paper and thrown after use. She want now to flirt with him and make him come behind her.
I dont mind even if they have sex once more, but I want them to make in front of me. Infact I want to have threesome. But She is not interested or She is hesitant. I dont want my wife to play hide and seek with me. While now I can’t even approach him or invíte him, since I have scolded him once. Now I am very Confused as to what to do?
My wife sometimes enjoy talking about threesome but says it is not practical and he wont even agree for that. Moreover we are relatives na! So She want to avoid any complication. Please suggest me what to do?