Fish deaths of fish I've come to know better are always sad for me. I'm not sad for week-old fry for example, as they do not show their colors or behavior much. But a month old fry, or even worse, a 3-months old fry dying, surely makes me sad. It's like watching something grow and then it's gone and it never got to grow fully either...Likewise. I went away for a week and came back to find that 3 of my neons are missing. Probably died and then eaten. Everybody was healthy before I left but these things happen, you can't be getting all sentimental when a fish dies! It's to be expected if you're still relatively new to the hobby but don't let it dishearten you - the more mature your tank becomes, the better it'll be at supporting life in the way of fish Keep at it, I'd bolster your fish's numbers gradually again (especially the schooling ones like the tetras), no more than 3 fish at a time and no more than 6 fish every fortnight.
And when a very old fish dies (such as my hoplo Seadra, dead at the age of 8), it's like I've been so attached to that fish that living without it is just not the same.