What did I do wrong

I meet my wife 20 years ago at 14 and I was love at first sight at 17 I asked her to marry me she said yes she got a job working in London getting a train every day at 18 she meet a let's say boy called William but he wanted to be called Dan ? She went out swimming with him one day did not tell me sent emails to each after saying how much they like each other when the for lunch one day the train stopped at eltham were he lived so he said I will drop you home so she got in his car and he kissed her after that he went back to Greenwich University that was in 2000 at a Christmas party at the end of 2000 she saw him he try's to kiss her she pushed him away I know nothing about all this in 2003 she meet him agian on a train six months before we got married he started to send her emails again we get married more emails and if a train was late she would bump in to him go for a drink with him for 10 mins waiting for a train 2005 we have a son 2007 we have girl 2010 we have a girl 2013 she leaves London work at home that's when she tells me not all at ones bit by bit lots and lots and lots of lies she said the last time I saw him was 2003 then 2005 then 2006 then 2007 what the hell she said I thought I had feelings for him but when we met again there was nothing between us and then apparently she was meeting other people for lunch s that she can not tell me about tell me about it I just feel that whole marriage and the whole life is a lie because of her in London it was a second life from me kids now I fill she told me because she can't get away with it anymore it is doing my head in 20 years together 16 years in London and I know nothing about it any advice