joined himself, etc. - his pride not yet humbled, unable to brook the shame of a return.
to feed swine - glad to keep life anyhow, behold the son sank into a swineherd - among the Jews, on account of the prohibition of swine’s flesh, emphatically vile! “He who begins by using the world as a servant, to minister to his pleasure, ends by reversing the relationship” [Trench].