What did Frank do when he came home from drinking after Amedee's death?

When Frank gets home after a day of drinking to find Emil's horse in his stable he searches his house and then gets his rifle. He walks to the orchard and then the wheat field, with no real grievance or plan. Then he sees two people under the mulberry tree. At first he thinks it may be the Bergson's farm girl. Then he hears what's going on and shoots.