Devastated Husband: Betrayed by Wife's Secret Chats With Married Man

hi I am a 38 year old guy happily married & have a 7yr old girl. My marriage had been pinch perfect in every sense. My wife is very loving, caring, always with me during crisis be it financial/ medical or emotional & my kid added the remaining stars to my happy life. I had a love marriage with my wife in 2013, we were in same office in 2010 where we met. It wasn't love at first sight, for 6 months we just had normal interaction like normal colleague, it was when she came in my team, we spent more time & fell for each other. Before taking any relationship any further, she enquired a 100 time if I didn't had any girlfriend before ( I didn't) & also confirmed from her that she didn't had any relationship in past. Infact, we started our relationship once we were completely sure that we are going to marry in future which we did. Before starting our relationship, she did told me that she wasn't a virgin as she broke her hymen by herself some time back (self enjoying). I completely trusted her as she had told me almost everything about her life & she didn't had any relationships & I found it a bit natural. We are quiet open with each other & dont hide any whatsapp/ mails etc with each other, they are always logged in in our laptops. 3 months back we had a fight due to some issue, I was working on my laptop where her gmail was signed in ( I use that a lot for my business as well). I looked at the chats link & found some chats of her with myself & a lot of friends. I enjoyed reading it, specially the part where we started dating. I didn't consider it as privacy interreference as we both were like open book. Suddenly I found a chat with one of her family friend in which there were lot of conversations like, tum meri jaan ho, I love you, Kiss you, aaj mil nahi paaye accha nahi laga, dono akele movie chalte hai etc etc from my wife side & that guy side. The guy was there family friend & was married, she used to roam a lot with him due to work ( atleast what I believed so before) & was very open with him. I didn't mind as I always expected them working together before they had fight due to some financial transactions. Now, I look back she was always with a guy whom she loved, not virgin & all my world just crashed down. It seems that I have been cheated from very starting from the very 1st hug to 1st kiss & 1st everything that I always considered was 1st for both of us & now feeling a lot of betrayal from the person I trusted the most in my entire life. I confronted her, she changed her statements everytime. 1st she said, her brother told her to talk to that person with love as there some money on hold ( not sure what else he would have told her to do), than she said thank god you found out, else I would have died in pain, saying she had a crush on him ( I found luv u & kiss u chats from both sides), then she said that he even try to ruin his married life due to her which his mother stopped & her mother stopped to take it further & several other reasons. But she has the stand that nothing happen physically, not even a touch. It's very hard for me to believe as I have always considered her to be completely truthful, honest & was sure I know everything. This incident felt me being betrayed & I am unable to trust her anymore. I still love her & we have our ever loving daughter but our marriage is no longer as it was before & slowly slowly its drifting apart as my behaviour has changed, I am getting anxieties remembering these again & again, I am unable to watch romantic movies ( which I liked before as I always used to imagine us) now I imagine her with someone that married guy, be it romantic movies, songs, even the dreams are terrifying. I cry a lot going to washroom or going to balcony at night but still am not able to maintain the same balance that we had before. Even she is trying to bring happiness like before but my thinking is completely changed. It's somehow effecting the kid as well as we don't speak with each other like we used to before & the kid understands there is an issue. We know we will save our marriage, but we don't want that. We want our life the same as it was 3 months back, not sure how to do that. Please advise.