after you make your cut, apply pressure perpendicular across the direction of the cut with your non-knife hand. this should keep the onion’s shape together as you make further cuts

There’s imo two solutions, one is to get a mandolin slicer

the other is to take the onion cut of the top but leaving the root bottom, cutting it then in half and taking off the first layer and cutting thin strips from root to stem making sure to keep the root end intact since that keeps everything together then cut it horizontally to end up with small diced parts, I don’t do the cuts you seem to do.

As for knives I don’t know which type of knife you use but a western style knife works best (the one that ends in a sharp tip), there I generally cut it with the tip of the blade not the ‘mass’ of it.

Also you can sharpen your own knife it’s not that hard and if it’s a fairly cheap knife just use the bottom of a mug to quickly hone the edge.

It eat it raw too. I mean, I put them in my salad raw, but I’m not going to pull own a pan and oil it up just for a salad. I’ve also given up on trying to be a fancy line cook that can dice everything in .005 mm cubes and just cut it the fastest way so it’ll go into my stomach

You can also try cutting the onion in a radial way. You cut the top, cut it in half, then instead of cutting with your knife parallel to the top cut, you go perpendicular and cut to about 1/4inch from the base. Then make cuts following the curvature of the onion all the way around and cut off the base at the end.

This keep everything together until the end, and you aren’t giving the side of your knife a huge surface area to stick to. Also let’s you draw your knife out instead of lifting

The crying comes from the onion irritating your sinuses. When I was a kid, my mom would make me hold a slice of bread with my mouth (so it would block my nose) when cutting onions and that always seemed to work.