I think your bofriend is acusing you of cheating because he wants to start a fight, thereforeeee it will make him feel less guilty of cheating. The extreme change in appearance and sex drive is also an indication of another woman. The excuse of working late is also the most common excuse for a man when he is unfaithful, and last, if your gut is telling you somethings wrong then listen to it. In your head you know whats going on but you feel that you need proof.