How many happy marriages do we actually encounter in this novel?

Unfortunately, not too many until we see the two older Dashwood sisters married off. Henry and Mrs. Dashwood seem to have had a very happy marriage, but we don't get to see it firsthand. Henry Dashwood has passed before the novel begins. Sir John and Lady Middleton seem to be happy together. This was probably not a love match to begin with, but they have grown comfortable with and seem to like each other. One can assume Lucy Steele and Robert Ferrars wind up happy together because they are such similar people. He doesn't seem to mind that she manipulated him into marriage and married him for his money. Marianne and Colonel Brandon will be happy together because she grew to love him and he loved her from the get-go. And finally, we know that Elinor and Edward will be happy together because they loved each other from the start.