سم الله الرحمن الرحيم
Bismillā hir Rahmā nir Rahīm
In the name of Allah, Most Gracious, Most Merciful
As-Salāmu `Alaykum (السلام عليكم):
Uhkti Xcoolamandax:
We perform du'a that this journey of marriage will be comforting and not a trial that you are unable to bear. I will assume you will receive the best advice on this forum and a overwhelming extension of du'a and well wishes. Insha Allah
Prophet Muhammad (SAWS) said that a man can marry for four reasons but advised to marry the religious woman or we will be losers.
Sahih Al-Bukhari Volume 7, Book 62, Number 27:
Narrated Abu Huraira:
The Prophet said, "A woman is married for four things, i.e., her wealth, her family status, her beauty and her religion. So you should marry the religious woman (otherwise) you will be a losers.
I will attempt to always put the best construction on a situation as all practicing Muslims should. Your Khateeba (Groom) to be might have suggested the weight lost for health reasons. Allahu 'Alim
The majority of the time anyone who makes an effort to change is because of a need. The suggestion that why doesn't he accept or marry you how you are is something only you and him can answer. Because you can always regain the weight. What will happen if you have children and are unable to lose the weight. These are issues you need to address and answer now.
That is really no ones business but you and him.