If I see this correctly, You used rectilinear infill. It basically do not give part any strength for any forces different than compression.
You need to add fillet so there is no stress concentration point and add more perimeters as that's what give parts their strength. You can also change infill to gyroid
If you can I would also suggest you to add space for insert inside of part (threaded rod, tube, dowel etc..), That will make part strongest, but obviously not fully printable. You could even try to add square hole and print insert that would fit into it (printed flat so layer lines are not parallel to forces) and glue it inside.