I've had some in my fridge open for about 2 months - its still in its sell buy date, however it says its to be eaten within 4 weeks of opening? What will happen if I eat it now?
It should be OK, especially since you've had it in the fridge. It's explained on this site
Personally, I've eaten peanut butter that's been stored opened and unrefrigerated that's been about a year old, and it's been fine.