NTA - first of all you don't actually have to have a reason to not want to date someone.

Second - your concerns about his weight are extremely valid and in no way fatphobic. I am a pretty big person, thought I dont want to say how much I weigh, trust me when I say its been some conversation with my doctors for years. Most of it piled on due to massive mobility issues from a disabilty, but I was already pretty big.

I watched my mom, who was overweight, though not as big as me, literally die in my arms as part of it. She refused to take carw of herself, and in turn that meant I took care of her. She too was only 60 when she died, and I was very young when she passed away as well.

Thats was my wake up call to force me to lose the weight no matter what, even if it takes years. And it has. I have gotten well over 100lbs off, and I still got a loooot more to go. Ive had to get many surgeries recently, and I am finally able to get up and move around and do what I need to do.

My point is, loving someone, but not wanting to watch them slowly kill themselves doesn't make you fatphobic. If you were fatphobic you wouldnt have been his friend. Toxic body positivity is an issue as well.

He is allowed to be whatever size he wants and you are allowed to not be with him because of that as well.