I've seen a lot of people kicked out for a lot less. The military takes that kind of thing very seriously.
You can report it to his CDR, the least he will receive will be a reprimand and have trouble making promotions. The worst he could receive would be getting kicked out after a courts martial with a small amount of jail time. Depends on the soldier, depends on the severity of the situation.
If it were just a fling, I would say move on, but a year? How on earth did you get suckered for a year? This guy should teach classes.