Sorry (albeit not surprised) to read this. I've developed a rapport with many of my fish like you did with Mango - evidenced by her acknowledgement of your presence and efforts to help right up until the inevitable end. In these cases, I know how heartbreaking it is when they pass away but how that is also combined with being worn out in exploring/trying every avenue possible. In time, hopefully you'll be able to reconcile this with knowing that you did everything you could for her in the time you had her. It's clear you'll make a good "fish parent" for the remaining 2 and any future fish you decide to get. Best wishes.