Your main job...Arrange the attire and manage your groomsmen.
That's right. This is your responsibility. Your soon to be has enough on her plate, so you need to make sure of the following...
1. Send your groomsmen emails briefing them on all formal wear information. Give them the list of places to get fitted, the specific date and time for pick-up, and a reminder for drop off to avoid late fees. To be sure get all information together, even phone numbers, addresses and detailed directions to the locations.
2. Assign responsibilities to your men. Delegate. They are there for you. Just make sure your fiance and event planner knows their duties.