Hi, welcome to the forum.
Does your son know the taste or smell of peanutbutter?
My middle son decided his younger brother needed to try pb. The little guy gagged, choked, vomited. So bigger brother was told to not give him it ever again. A few years later, brother decided to try again....with same result. I didn't actually think he was allergic to it....I thought he just really hated it. Testing showed no peanut allergy. (He has non-food allergies.)
Anyway, I'm wondering if your son just doesn't like it.
~~~
As for whether you made a mistake by letting him know how serious his allergy is....I think he needs to be aware of how serious it is.
Again, with my youngest, he was afraid of everything. (Seriously....everything.) he was terrified of insects. So, we didn't feel the need to go into detail about how serious it could be if he was bit or stung. (Yes, he's reacted to both bites and stings.). He was being teased at school, and we practiced at home how he should tell a teacher when it happened. So, at morning recess when a kid was teasing him he went to the teacher on yard duty and told what was happening. When the teacher didn't take it to seriously he explained about being allergic, and showed her his epi-pen. She went to the other kid, and in her lecture used the word "bullying" and said "this is nothing to laugh about. HE COULD DIE IF HE GETS STUNG!" And my poor little guy was stuck at school all day, and when I picked him up he asked if it was true he could die from an allergy. Poor guy. That was definitely the wrong way to find out.