Why and how did Partridge married Molly?

There is only one mention of Partridge's marriage or plan to marry Molly in the text. This quote can be found in the last chapter of the novel.

As for Partridge, Jones hath settled L50 a-year on him; and he hath again set up a school, in which he meets with much better
encouragement than formerly, and there is now a treaty of marriage on foot between him and Miss Molly Seagrim, which, through the mediation of Sophia, is likely to take effect.