We Lost Contact and She Cheated on Me and Slept With My Friend

I am 29 year old guy and I just graduated from the university. While in school, I had a group of friends who we were very close. Everybody knew us on campus as we looked inseparable, because we were always seen together and did things in common, although we were not all in the same faculty.

When I was in my second year me and my friends invited some girls over to our house outside of campus. We all got paired up with the girls and we all succeeded in sleeping with our partners.

For a while I continued to date the young lady I was paired with while my friends just quit theirs after succeeding in bedding them. They were all pressing me to let this girl go since they had gotten rid of theirs.

I did not agree with them and continued with my affair untill I finally graduated. It is a year now since I left the university, but I have not gone for my national service. For this past one year I  partially lost contact with my friends because we were no longer in school.

Even my girl was among those I lost contact with until lately when I got a shocking revelation. About two months ago I managed to make contact with her and we started our affair again. At this time I was also communicating online with my old friends and while chatting with one of them, I informed him about how me and this girl were back together again.

This friend of mine then told me how one of our friends too had slept with this girl of mine soon after we graduated. I was shocked at this information and had no reason not to believe him because indeed during the last phase of my studies, I had really distanced myself from affairs and friends so that I could concentrate on my studies.

The problem now is that I am still seeing this girl regularly but all the feelings I nurtured for her before now are totally dead. I have not told her about what I learnt because I am thinking of the best way to get back at her, to punish her for cheating on me.

As for my friend I feel he has betrayed me and this has definitely caused a rift in our friendship as I have blocked him on all my chat and social networks.

Please I need advise on the wisest thing to do right now because I dont want to do anything foolish. Should I find a way to punish this girl and my good friend who betrayed me or should I just let it be and cut off my relationship with both of them (my girl and my friend) and move ahead with my life. After all I have stopped having any feelings for this young lady. Help me.