Alma 31:2

for it was the cause of great sorrow to Alma, to know of iniquity among his people; therefore his heart was exceeding sorrowful, because of the separation of the Zoramites from the Nephites.

It made Alma very sad to know about the sin among his people. He was very sad because the Zoramites had left the Nephites.

Nothing grieved Alma more than seeing his people turn to evil. It broke his heart to know the Zoramites had split away from the Nephites.