Seams coming apart - some causes
Usually my seams do not come apart - any more -
Some things that have caused problems for me:
The seam allowance got too skimpy!!! It really is better to unsew the seam and sew it again properly.
The fabric was a frayer and/or flimsy.
The fabric was very loosely woven.
Using an overly long stitch length.
I was trying to "fudge" a skimpy piece to fit - and that resulted in a skimpy seam allowance - and that resulted in the seam pulling apart.
The fabric gave up after being unsewn and resewn several times.
When strip piecing, did not shorten the stitch length, so the units came apart before I got around to incorporating them into bigger units.
Not stay-stitching around the outer edge of a pieced border.