My fiancee had a double life for more than 7 years and he is cool about it??? !! Help !!!!?

I found out that my boyfriend had a fake facebook account, a fake msn, yahoo messenger, Skype AND badoo. In the beginning I was suspicious or had some small clues. He kept on saying "it's not mine, I am innocent, I am honest, I don't know anything, it's the account of a friend". However, I finally found out that it was his ! I saw his accounts logged in on his phone etc! I have proof now!! When I confronted him he was like "it was nothing, just for fun, I was bored, I did chat only and no sex, I love only you". He had been doing that for 7 years behind my back !!!!!!! And we are together for 10 years !!!!! And he proposed 4 months ago! Please help me!! I love him but I don't know what to do !!!