well i gotta say that thats close to my story but i think mines is worse, i do think its ED but you have a small case of it. personally, i think so becuase after a min of no contact, it should still be up and ready. im 18 and play football, great shape, no alleregies etc... but the same thing still happens to me
OR...
it could just be all in your head that once she stops the contact, your intamitcy drops, you dont see her as sexy as when shes touching your, or something to that extent
just trying to help..