What does the bike feel like when you ride it?
That appears to be a cracked weld. And, little things like that often make big things. JB weld won't do anything.
If you clean (electric wire brush or sandblast) the frame spotless for about 1" on all sides of that crack, then a good welder should be able to weld that up in about 5 minutes. Then repaint, or leave it as a battle scar.