Chapter 3's most important events are Ben's two meetings with Marla, his resolution to try to hook up with Dallas, and his dreams about talking with Jesus.
Here's a more detailed summary:
The chapter takes place in late August, as Ben is talking with his therapist Marla (who's specifically a psychiatric social worker) about his plans to participate in football.
He's witty and playful with her, but in his mind, he reconsiders his plan to not tell his family about how he's going to die soon. Ben feels frightened and unsure of himself, but he also feels curious about the whole situation. He considers how he might pack a lifetime's worth of experiences into a single year, and about how, in terms of other living creatures and the history of the world, a year of life is paradoxically both an amazing gift and something practically negligible.
Ben jokes with Marla about condensing his life into a single year, then asks her to reassure his doctor that he's fine and still doesn't want medical treatment. Ben asks for Marla's help in a romantic matter, too: he's desperate to hook up with Dallas Suzuki, his crush.
After the meeting with Marla, Ben attends football practice, which is as vigorous as ever. He heads home with his brother Cody in Ben's beloved pickup truck, and they chat happily about football.
In another meeting with Marla the following day, she tries to convince Ben to get medical treatment. He distracts her by saying he wants to discuss a dream he had about having conversations with Jesus, whom Ben calls "Hey-Soos." In the dreams, "Hey-Soos" and Ben talk about what Ben might do with his remaining life, but "Hey-Soos" doesn't make any suggestions or give Ben any particular instructions.