In a way, this book is staging a whole debate on the institution of marriage. Hardy does not necessarily suggest that marriage is automatically bad, he just makes it clear that he believes people should be able to step away from a marriage if things do get dire. He also makes it clear that marriage is not necessarily linked to love in any way, so it's obvious that a decent, understanding society would accept Jude and Sue's relationship because they truly love each other, regardless of whether they are married or not.
While Sue's views on marriage were scandalous at the time Jude the Obscure was published in 1896, they seem fairly tame and uncontroversial now.
Jude's second marriage to Arabella—after everything that has happened between them—appears so over-the-top and ridiculous that the novel slips from realism to soap-opera-style melodrama at that point.