Thanks for the informative link.
In this section St. Thomas is writing about the reasons why marriage is indissoluble. He asks, "What sort of friendship should there be in marriage?" and answers "the greatest." And therefore that is one of the reasons why marriage is indissoluble.
The title of the thread perhaps accidentally gives the impression that he is comparing friendship in marriage to other sorts of friendship, which is not what he's doing in this section.
He says that between man and wife there should be "maxima amicitia." But he doesn't make any ranking of that maximum friendship compared to others.
