I agree with Woog on that. So if you love him, then say ILY. If you don't, don't lie. You need to tell him what you are thinking. Letters are good. You know how to write constructive letters to him. I would explain the quandary to him. Maybe even send it while he's away. He probably has as much time to think when he's away as he does at home. I would be honest with where you are at. What do you gain by hiding the truth about your relationship from him?
