Based on the history of the boss not fulfilling promises for pay raises and only showing interest in giving a raise when you mention leaving, it may be difficult to trust the boss's word on the potential pay increase. It is important to weigh the pros and cons of staying with the company and consider how the situation may affect your future career growth and satisfaction. Ultimately, the decision to stay or leave should be based on your own judgement and what you believe is best for your career.