How does Bunky find out about Eldon and Angie?

Chapter 21 witnesses Bunky, Angie, and Eldon all sitting in the harsh light of the kitchen. Bunky is glowering, repeatedly slamming his fist on the table. Finally Bunky asks, “This is how you repay me?” Eldon apologizes, and Angie says that it wasn’t Eldon’s fault. Bunky stares at Angie and tells her that he loved her, trusted her. Bunky asks Eldon if he loves Angie. He says he does, saying yes once to the floor and then meeting Bunky’s eyes and saying, “yes.” Bunky asks Angie if she loves Eldon. When she says yes, Bunky breaks. Bunky falls against the door jamb and puts a hand to his face.