I had a problem similar to this several months ago. Eventually, that group ended up not working out (for -other- reasons) but with my new group, I had gained some experience in some little things that I would and would not tolerate. The first thing I put on that list was: "The monsters are mine, not the Monster Manual's. If I say that XXX monster has YYY hit points, even though the MM says it should have ZZZ hit points, it has YYY hit points. If I give a monster a nonstandard ability, it has that non-standard ability. Just because you've seen dozens of these monsters in other games you've played means nothing about THIS game."
In such a case, if one of my players told me that something had XXX hp left and that he'd been keeping track, I'd ask him how he knew what number to start with. If he quotes the MM, I'd just smirk and move on, and if he pressed that point I'd say I advanced it, or modified it. I'd say this EVEN IF I HADN'T, HE WAS RIGHT, AND I WAS WRONG. Because the DM isn't allowed to be wrong. The DM being wrong creates situations like this, where things are disrupted and no one is having fun anymore. If he said that he knew where to start because he'd noticed how much damage other eye stalks had taken, I'd just mysteriously say things are happening that he knows nothing of.
If he pressed the issue further, he'd not be in my group any more. And the rest of my players would support that decision.
That's how I'd handle things, however. Your situation is a little bit different. He apologized, realized what a jerk he'd been. I'd give him a second chance there. I'd also, at the beginning of the next session, lay down the rules where it comes to "DM accountability". Something like what I've listed earlier. Say it outright, and if everyone agrees (I can't imagine them not) then you can keep going.
As for your emotional control, I totally understand that issue as well, and if you have any problems, ask your group for one week where you guys do something different. When I'd had a REALLY REALLY stressful day I informed my group that night that we were going to play some cards before the game (Mao, to be specific) otherwise I wouldn't be held responcible for the nasty things I was going to do to their PCs. I think it was important to do something else WITH THE GROUP, because that allowed me to work out my feelings with them around. If I'd just stayed home I wouldn't have been thinking about issues and things.
Hope you don't give up the mantle of DMing. Hope you work your problems out. And good luck.