What transpires between Christian and Lissa in the attic in Chapter 18?

Lissa flees to the attic to cry in her depression. Christian walks in, and they begin to argue. Christian tells Lissa that Mia hates Lissa because of Lissa's brother. Lissa's brother used Mia, then left her, breaking her heart. Lissa adores her brother and will hear no ill of him. Christian kisses Lissa, but she is angry at him for what he says about her brother and tells him to leave.