Briseis, I read your original post almost immediately after you created it. I refrained from responding, yet I feel compelled to do so now.
You seem to be a patient, loving girlfriend. You are willing to go to significant lengths to spare your beloved any discomfort. You do not wish to pressure him. These are noble and commendable desires. However, it is wholly understandable for you to be affected--even profoundly--by his unwillingness to marry you.
I will not delve into the reasons, yet I was in a relationship wherein I was in a constant state of limbo, seemingly without a defined or even general end. Although we had reached the point of engagement, we were not moving forward and it was due to certain actions (or lack thereof) on his part. In my endeavors to be patient and understanding, I endured a situation that was both unhealthy and painful. I had no idea how damaging the effects of this limbo would be, yet they struck me to the core. Although I did not lose respect for him as a human being and brother in Christ, I lost respect for him as a potential husband.
When a man passionately loves you, you should never have to light a fire under him to marry you. He shall willingly embrace the opportunity to dedicate his life to you, despite any and all fears.
I know that you did not come here to criticize your boyfriend. I do not pretend to know his heart and hence it is not my intention to unjustly assess the situation. Yet whatever his reasons, this man has left you in a state of limbo for a long while and it is unfair to you. Of course, you must determine how long you are willing to wait.
Insofar as his desire to lose weight--as a woman who has struggled in this area, I can truly empathize. However, I would never refuse my beloved's longing to marry me, thin or not, because I adore him and deeply desire to enter that sacred covenant with him. If you accept him as he is, and he has been willing to enjoy the benefits of your company and love as an overweight man, why is he not willing to do so as your husband? What if he cannot lose all the weight by October, 2010?
I pray that he will keep his word to you regarding this general timeline.

When I hear or read of similar situations, it grieves my heart. We as females appear so willing to wait and wait for our men to be prepared, for our men to come through for us, even amidst our pain at their constant refusals. Far too often, we are willing to wait longer than we should.