what do i do

You are in for some tough times, yes you will have trust issues about if he is faithful to you or not,but if you trust him and he you then you just have one less issue to deal with.As far as the what to do part is concerned,you can do nothing but to encourage him,write as often as you can they tend to get homesick and lonely and the army sometimes tends to change them but do not worry he'll still love you maybe even more and what ever you do don't be mean to him on his bad days or any day for that matter.because while he may appear strong and act like it don't forget that he is a person with feelings.hang in there.

P.S i have not seen my fiancee for over two years now and it's tough but it's worth it.