Why doesn't the narrator cry when Marla attends the support groups he does?

The Narrator knows he is faking his diseases at each support group, but he goes anyway because it helps to alleviate his insomnia when he cries. The narrator first sees Marla at a testicular cancer meeting and knows she has never had testicular cancer or testicles, and is thus faking. Marla reminds the narrator that he too is a faker and, as a faker, she mirrors his lie.