I'm pretty much of a Christian, too, and I usually turn to prayer when I've got absolutely nothing else to fall back on, but in this case there are plenty of resources for you -- counseling, medication, support groups like this one. My feeling is that if God gave us an intellect, he would want us to use it.

Your irritation at your brother's smugness probably just eggs him on, but it sounds like his belief system is really pretty fragile if he can't even engage you in a reasoned debate. Even after all these years, I still try to reason with fanatics, though I should know better by now. Eventually, something may come along that shakes him to his core and wipes that smug smile off his face.