I second professional help, but I want to add a little about why. This seriously sounds like there could be something off with his brain chemistry. The longer he obsesses, and thinks the same thoughts, the more embedded the thoughts and the neurons become. The sooner you get help, the better chance you have of 're-setting' back to some kind of normalcy.
This is not about the food.
Love is that condition in which the happiness of another person is essential to your own...
Robert A. Heinlein
Me: female, bi, (formerly hinge of a vee)
with FirstBoyFriend (FBF)(moderately long-distance)
and no longer with CurrentBoyFriend (CBF)(who now lives in a house far away-with stairs I can't climb)