What to write in my Letter?

I am writing a letter to My ex. But it isn't a spiteful letter.He recently went into the Air Force and I haven't had any contact with him for since he went in. My friend says I shouldn't write what I am feeling. She says I should just write a short cute letter. But I am stuck and don't know what to do. But, I am still In-Love with him, and he already knows that but he has moved on even though I know he still has strong feelings for me. I don't know what to do, Please help?