How is life with a companion animal not a relationship? I wouldn't partner with someone who could discard a cat or dog on a whim; that would tell me all I needed to know about them. And many animal "allergies" are a more acceptable cover for dislike.
There is something to be said for marrying young, I suppose, from the standpoint of growing up together. Although you could just as easily grow apart. Marrying doesn't suit everybody, anyway.