Hey there bouncy... if you have been reading this thread and considering the discussion here then I have a feeling that you not keeping up with your fiancee is not so much about what you have eaten, but possibly about your endurance fitness.

Eating def does help performance, but unless you are used to doing the miles, then your body just won't go the distance, no matter how much you tell it too. Maybe your fiancee can do a longer loop, and ride with you til just before you get tired, and you can head home at a slow warm down pace while he rides on and then catches back up with you?