Laurie in the first half of the book, Professor Bhaer in the second, to be honest.
Little Women was originally published as two books: Little Women and Good Wives. In some places it is still published this way, but in most modern US copies of the book they combine the two, usually labelling them parts one and two. Little Women, the first book ends just after John Brooke proposes to Meg. Good Wives picks up a few years later presumably when he has earned himself enough to support Meg as promised.