That area is very soft and easy to tear, especially if he did not thrust straight. Typically this gets torn during rough sex and sexual assault. Friction can also cause this to tear.
If it does not get better, you have to see your doctor. Normally it will however heal pretty quickly by itself it the tear is not deep.
Keep is dry and clean. Wash yourself with water after toilet, rather than wipe. And pat yourself dry. Sleep without panties if safe. Only wear Cotton panties to keep you dry.
Take care!