"In my case, sugar craving roars back if I indulge,..."

Me too! But that iron grip is still as strong as it ever was. 

I previously struggled with food addiction before that, so I kinda wonder about that ...

I have always been a meat and potatoes type.  I never really ate between meals, and I would get the 20 oz ribeye instead of the sixteen and bypass desert.  Now that my diet is very high in protein, and very low in carbs, I have a wicked sweet tooth.  I have had it since a coupe months out.  It really bugs me but I can live with it.  I eat some no sugar added ice cream occasionally which seems to do the trick.  I just wish I didn't have it at all.

I work for a guy that is in tip top physical shape (no WLS).  Gym six days a week, eats very healthy, only carbs come from fruits and veggies......he switched to that life style about 10 years ago.  He told me he has the exact same craving as me.  Just one bite of a donut, or something sweet makes it go away.  

I have often wondered if this is psychological or physical.  Probably just in my head.

What we eat alters our hormones and neuroendocrine response.  It's not bypassing so much as habituating the neurons via diet changes.  For example, gastric distention is now being studied at Purdue, because to consistently overfill the stomach is now becoming known to alter these neurological pathways.  Artificial sweeteners, and sweet tastes, have also been known to have an effect on the brain.  So it's probably a combination of neurological/gastrointestinal changes that happen due to dietary restriction.