My fiance just had his routine checkup and his blood work came back normal except for he has a lot of enlarged red blood cells?

Macrocytosis. Macrocytosis (mcv >100) is commonly due to vitamin B12 +/- folate (folic acid) deficiency. That's next step in evaluation. Luckily, both vitamins are inexpensive & available in large enough doses as a pill (even w/severe gastritis). Shots aren't considered necessary to treat low B12 anymore as 1, 000mcg daily can overcome lack of intrinsic factor. Btw, macrocytosis often associated w/excess alcohol, low thyroid.
Vitamins. He may be deficient in Folic Acid or vitamin b12. This sometimes happens with certain parasites (like tapeworms) or diseases (like pernicious anemia). However, in the United States is much more commonly associated with alcoholism.