How to save my marriage after cheating my husband for 5 years?

I am married for last 8 years and a child of 7 years. I started loving my husbands friend 5 year back and having with him.he is 18-20 year older than me. My husband found out and is heart broken,ask many quesions why i did with him. I have no answer. I ask him to forgive me and pardon me. I was tricked by friend in the name of missing love in our marriage. now i feel what a stupid I was? even his wife knew, and gave consent for our relation ship. My husband is not able to believe that this was happening to him, but says he still love me and trying to save the marriage as it seems is worried about insult to him in the community, if it goes other ways. I feel very sorry for his mantle state and stigma i have given to him.he has got many of my love letters , which he keeps reading and at time cries. Talks about divorce but is not sure due to our child.Now I really feel guilty what i hv done, I want to save my marriage and want to prove that i love my husband and past was a mistake.