What is happening between MARLOW and KATE in act 5?

Kate enters almost right away, and the two elders interrogate her. When she answers that Marlow did indeed meet her more than once and spoke in effusive tones, Sir Charles is certain she lies, since he knows his son's manner to be "modest." There is an irreconcilable perspective amongst them, so Kate proposes they all meet in a half-hour, and the men can listen behind a screen while she confronts Marlow. All agree.

Once he arrives, Marlow again laments his situation, where his passion is enflamed by the grace and appearance of this girl who lacks the fortune to please his father. He insists he must quit her immediately, and she grants him this, herself sad that "all [his] serious aims are fixed on fortune." He assures her fortune was not what drew him to her but rather her qualities, which he is learning to see as "refined simplicity." Through his speech to himself, he resolves to stay with her despite his father's lack of approval. She refuses him, claiming such a union will surely result in resentment, but he claims otherwise, and gets down on one knee before her.