Getting numb to it and overloading because of it are two completely different things. You blow your top when you're repressing all the little things until they boil over. If you're numb to it, the bad shit just becomes part of daily life and you don't even notice it.
On that point, yeah, I've definitely become numb to some things. I've gone through so much terrible shit involving my son over his seven years of life that when something bad happens involving him, it doesn't even phase me, I just deal with it.
Case in point, last week we got a call from his school during the day that he went missing. According to the recess supervisor, he ran off when the bell rang, and he couldn't be found afterwards. My wife went hysterical, police were called, we all start combing the area. I know he's lost, because he reportedly ran off completely in the opposite direction of home, and I drive him to school every day. After about 20 minutes of this, I get a call to come back, they have him at school. Turns out he was in his class the whole time, and no one actually checked there. It was some other kid that he was playing with that ran off, and that kid only lives a block away from the school and was also accounted for.
The point of that story is that during all that, none of it phased me. I never panicked, I never went nuts, never got worried, I just did what I needed to do to best find him. The whole situation seemed odd, because he's not a runner, and desperately wants to be near an authority figure at all times. Being lost and alone, I used what I knew of his behaviour patterns to find places to check. I was still relieved when he was found safe and sound, but at the same time I never actually got that worked up in the first place. This was just another checklist in the neverending shitshow that this poor kid's life has been. It doesn't really phase me anymore when something involving him goes wrong, its just easier to figure out how to fix it.