Through the end of act one, a lot has unfolded. The biggest surprise was Linda revealing that Willy was suicidal. Earlier in the play, Biff and Happy believed that his driving problems were caused by Willy being too easily distracted, but Linda told the boys that investigators of one of the accidents saw that he had crashed the car on purpose. To confirm this, The Woman was a witness and saw him driving at a normal pace with plenty of control and he suddenly drove into the side of the bridge, and only the shallowness of the water saved Willy's life. (So, Willy wasn't having an affair either.) Not only, but Willy has been inhaling gas from his heater using a small length of rubber pipe. Linda was too ashamed to show she knew about it to move the tube. 
Everyone knew that Willy was stressed from his age and his money problems, but only Linda knew that he was that bad. His own sons just thought he was going crazy. Once they see how upset and worried Linda is, they decide to stay home instead of moving to the west. So clearly they are more loyal towards Linda than Willy. Even though they used to be in awe of Willy, they still have little faith in him. The act ends with Willy reminiscing about when he was younger and Happy was on a team. This is a very important confirmation, that Willy's depression came because he isn't as young, successful, and respected as he used to be.