You're going to want to do two things here in order to fix it: Get yourself some reinforcement and learn the shoelace stitch.
First, that sheer fabric is just going to keep ripping if you sew it on its own, so you need some bias tape. Try to match the color as best you can, but don't worry if it's a little off. This will just help to cover up the sheer fabric's raw edge and make it a little stronger so that your new stitches won't rip out. Place it right along the ripped fabric so that the edges line up and sew it right over the top. Then you'll have a double layer of fabric to work with. :yes:
Next, you can bind the two parts back together using the shoelace stitch. If you make it small and tight enough, you won't even notice it once you're done.
It looks like this:
You're essentially pulling the thread under and then over each fabric edge, pulling it tight in the center. Trying to do a regular running stitch might end up pulling your shirt too tightly, since it doesn't look like you have much room for seam allowances anymore, so this is a good alternative that won't mess with the way your shirt fits.
