Theodore lied to you. He pretended to be nothing but a university student and your boyfriend who caught an illness and was about to die. His true objective was that he wanted to find someone who wouldn't like him just for his money. And he found you.

As Theodore pretends to have this illness, he lies in bed, waiting for you to feed him whatever you make. He slips up a bit though, forgetting to cough a lot and made you ask if he's getting better. He suddenly starts ( fake ) coughing again.