To start off I know I am slightly over reacting but to what degree? 

So my S.O needs to mail some tax stuff, asked me to write out the address for him because I have legible handwriting. I wrote out the address fine except for one thing (an extra letter in the city and we don't have an envelope on hand) . It was really dumb tbh but im super OCD about little things like this. I said it was really bothering me but left it at that. 

I started doing my thing and not even 2 minutes later I asked if we were leaving soon, he replies "well I was going to mail my tax stuff." 

Immediately I go into defense mode (which I where I overreacted I should have stayed calm) . I ask him "how are you going to sit there and make a joke about something like that after I just said it hurt."  He said "you moved past it because you were doing something else" and I replied "I explicitly told you it upset me why" and it just kind of ended there 

This has been happening alot lately over really silly stuff. Am I being a big baby or am I rightfully defending my feelings? Is there a medium? I just don't want to continue on this path and I want to heal and be happier.