3-3: caerme de espaldas: to fall on my back.
3-4: había de conocer = conocería. Haber de followed by the infinitive denotes (a) obligation: as: ha de ser, it must be; habrá de hacerlo, he will have to do it; (b) futurity (present tense of haber de + infinitive), as: he de hablar, I will speak: (c) conditioned action (imperfect of haber de + infinitive), as: quién había de creer? who would believe?
3-5: que haya madre: and (to think) that there should be a mother!
3-6: Jesús: the Spaniard, the most Catholic of men, is in the habit of interlarding his speech with copious expletives derived from his religion, such as Jesús, Ave María purísima, etc., which may often be rendered by the mildest of English substitutes.
3-7: ¡Que ... muera!: may I die! let me die! As the subjunctive used with imperative value, depends on some desiderative verb understood, the que which would follow that verb is usually retained in Spanish (as in French), though not when V. or VV. is used.