Kylo's tantrums are actually panic attacks. No one ever taught him how to deal with them which is why he goes nuts and starts trashing the place when they hit. Hux eventually figures this out and slowly learns how to calm Kylo down - talking to him patiently in a quiet voice, petting his hair, snuggling and assuring him it will all be ok. Once Kylo has calmed down he proceeds to fuck him so hard he's too tired and sore to move. Kylo goes off to sleep happy and Hux can relax knowing his ship will remain intact for another day...