We've learned thru 2 years of trial and error, back and forth, that it's almost impossible to judge reactions and how you feel when dealing with MS and supplements. Because of the nature of MS, some days are just better than others, for no rhyme or reason.
Your boyfriend's fatigue is not related to his B12 supplements. It's his MS. Fatigue is the most debilating part of MS my husband has and his B12 levels are super. After his first flare, he used to fall asleep just sitting, talking to me. He had a car accident when he fell asleep at the wheel. He now takes daily provigil and quercetin and EGCG supplements to aid his energy and is much better.
That said, the best thing to do is put together a supplement and nutritional program that addresses any imbalances you find on blood tests. Have B12, D, uric acid, minerals and hormones tested regularly with his comprehensive blood tests. Then you can see if the supplements are having an effect. Overall, you should see a halting or slowing of progression. ( The program I put together for my hubby is highlighted in blue below...click on the link and you'll get to a hosting page with my paper for free.)
Keep researching, eat healthy and fresh, keep him moving any ways he can, keep laughing and finding joy.
wishing you answers-
Husband dx RRMS 3/07
dx dual jugular vein stenosis (CCSVI) 4/09