The ECO is right, as far as UK rules go I think it's a max of 6 months in any 12, but if the ECO is aware that you are in a relationship here my guess is they are now telling you it's Spouse/Fiancee visa time.
The only way around it is to try and appeal and explain the problem in every single detail, and if that fails your other half will have to visit you until you are ready for the Spouse/Fiancee visa.
