Is my husband cheating?

My husband is in Afghanistan on his first tour.We have been together 8 years,married 3.We had one fight about something stupid and he started to not call on skype,no answer to my emails, stopped saying i love you.He came home for his R and R in November and filed for a divorce.He did not tell me. He had mentioned separating when we spoke on skype before he came home.Everything was ok then all of the sudden he stated saying he was not happy and that he has grown up in Afghanistan. We are 12 years apart in age, I am older. I have 2 kids from a previous relationship and we have a 3 yr old son.We fought quite a bit the last 3 years about money etc.before he deployed he wrote me the sweetest letter about how we would be together forever, he sent me flowers a month before he began this change. We slept together when he was home yet he stayed at his fathers, he slept with me the last night he was here and had filed papers the day before.He even changed his email password so i cant get into his inbox.Eveyone we know is thrown by his behavior, most say he is cheating. Please help me!!!!