How can I reassure my boyfriend I'm not cheating on him?

Back story, in his past relationship he was cheated on a lot, by the same person. And he stayed with her even after he knew. And she manipulated him, and brung up stuff from his past that he forced himself to forget, ect. she was just crule to him, and used him for his self gain. So now he thinks I'm constantly cheating on him, but in realitly I love him and wouldn't do anything to hurt him, he wants me to get a job (which I'm working on) but he wants me to get one just because I won't be bored so I don't cheat on him (problem with that, he wants me to get a job i know I'll hate, but if i wait a few months (which is ok, cause i don't need the money) i can get a job I'll love, make more money, and it will help me with my future). How can I reassure him I'm not cheating?