How can I divorce based on adultery?

My husband and I got separated after a year married when I got messages of another woman on his phone. I felt depressed and he would come round to my place talking afvantage of the sitaution for sex. I was so depressed that would eat only when would come round and he would have sex.. It was humilhating and destoyed my seld esteem. Today I see how evil that was. After a year I went to study and work and had no time for nothing else, I was finally cured of the depression. But I needed him to sign for me to rent a flat, so the flat was in our both names. For 5 years no the flat is still on our both names. During this period of 5 years we were friends but no sexual, however he always said he was single to me, but recently I found out that he was living with another woman 3 years and bought a flat and never told me. Anyway. Now we have been married legally 7 years. We managed to become good friends in the last 2 years. But the things I recently discovered stunned me, and I asked the divorce kindly. However he said he would not agree. And would say we been living together all this time since the flat was in our both names. He was living in Beirut on work the last whole year, and now published pictures with a girl in his face book on holiday 6 months ago. When I mentioned of the girl, he said she was a friend! So we are divircing and I just wanna this to be quick, I am very disappoited of who he turned into in the last two weeks. I am not in love with him, I have a boyfriend for the last year, and I am moving on into my career now. What I am worried is that I am to do an online divorce tomorrow, and the only option that suits available is adultery, but he can deny that, so how does it work, any experience?? what if he says we have been separated for all this time just to put me in a position of lier? I will get in trouble? I just want this nightmare to end...... please advise me. Thank you.