Is it normal to cry over a goldfish dying?
Of course you are not a weirdo! It may have been ‘only’ a goldfish to some people but it was your pet and whether it had fins or fur doesn’t mean it should mean any less to you. Cry as much as you like because it is a NORMAL way to deal with shock and sadness. But don’t think too much about why it died, knowing won’t bring it back and blaming your brother won’t help. The water may have been warm because the room was warm, no neccessarily because he put in warm water. It is normal to think about why someone died and to wonder if there was anything that could have been done or not done to prevent it, but death is a naturlal part of life and has to happen, no matter what the reason.