I need help ASAP

I have a second hand classic 350, and a crack seems to have developed in the rear swing arm, the footpeg and side stand were moving a bit. My question is, why does this develop, and will welding it fix it permenantly

I have a second hand classic 350, and a crack seems to have developed in the rear swing arm, the footpeg and side stand were moving a bit. My question is, why does this develop, and will welding it fix it permenantly