First of all, congratulations on your weight loss so far!
I am so sorry your grandfather was so insensitive and ugly to you about your weight!! That was a very unkind thing to say and I am sorry that you stumbled off plan due to the emotions it brought to the surface
However, now is the time to pick yourself up, dust yourself off, and MOVE ON. Yes, it was hurtful, yes he was wrong in saying, yes what he said was blatantly untrue....
...but what are you going to do now? You have a choice. You can mull it over in your head, add some of your own negative dialogue with it, keep replaying it, feeling worse and worse until BAM you are back at your start weight...
... or you can brush it off, chalk it up to the nonsensical ramblings of an old man (no offense to gramps) and get back to the plan and vision you have for YOUR life.
Good luck on your journey *hug*