Is there any way that you could periodically excuse yourself & go out for a walk or something, when you start to feel the stress building up? It might give you a chance to breathe & relax a bit. Emotional detachment is really hard face to face, so you shouldn't beat yourself up if you find yourself reacting - what's done is done, so let the moment pass & try to avoid anticipating the next time it may happen.

And if venting here helps, then vent away.