the sensitivity of your nerves can't be helped (without the dubious practice of conditioning)- some people naturally feel pain more than other people. However, what really matters, particularly in boxing, i how to deal with pain and how you react to it.. This part is 100% MENTAL - Now Man up.
Then I have to say, I don't think you've ever sparred/fought anyone decent in boxing. I haven't had any fights yet, but I done two years sparring in Muay Thai and I've done a year in boxing and the boxing sparring is ALOT harder
I wouldn't read too much into it - when people hear 'muay thai' they automatically think of some bloodsport ****. In reality, although the guys in Thailand are pure tough, it's just another kickboxing style.