[Rant] Could use a pep talk, some expletives inside. Really frustrated!

Hi guys, I've told others to keep their head up and press on in the past and was wondering if anyone could return the favor.

Here's the situation: I have a reef tank that I troubleshot and troubleshot to get stable and get some growth out of my coral. It's now what I would consider mildly successful, in that I've only lost one coral recently and regularly rehab bleached or dying corals from my LFS. HOWEVER, a problem has arisen with my fish. In July, I lost four of my six fish, set up a quarantine tank and reevaluated my process of adding fish to the tank. I thought it was disease but now I'm not so sure. Since July, I've added five fish, and only two have survived (my melanarus wrasse Kai and my banggai cardinal Larry Bob). I've finally narrowed it down to my FUCKING blenny, my oldest fish in the tank, who had suddenly become territorial for whatever reason. I saw him attack a goby that I added in early August and thought it was just an issue of perching fish (I had "mysteriously" lost a flame hawk earlier in the summer - the first of my massive losses, now I know why). But this little fucker just brutalized a cherub angel that I added - things were going fine all night and in the morning, but this evening the angel's pectoral fins were ripped to shit and he's looking really bad back in the qt. My wife and I ripped apart the tank and got the blenny out, he's in a one gallon awaiting deportation to the LFS tomorrow but I feel really frustrated. It's far from the worst case I've read about on here, but I feel awful about leading new fish into an ambush and not knowing enough to prevent this bullshit. Fuck! Could really use some perspective, am feeling pretty damn dejected and that I should've known better. I really tried! Tons of online research and talks with LFS employees and even looking through my copy of The Conscientious Marine Aquarist. All to no avail and now I'm back to square one. Ugh. Anyways, thank you to whoever took the time to read this. Shit happens, and today it happened to me. Good luck and godspeed in all your fishy endeavors.