“As proof of that you cited the fact that Yitzchok loved Rivka after they married, not before.”
That does not mean that love does not come before marriage, only that the love that comes FROM the marriage is richer and has more substance. Plenty of people fall in love and then get married. The commitment of marriage deepens those feelings, but it doesn’t mean they are not there on a high level for many of us, prior to the wedding.