Have you actually asked for any promotion / pay raise in the past two years?
If not, don't be so surprised that this is the first time your manager mentions these. They rarely throw these at you without you asking. Offering them now may simply be an honest sign that they want you to stay.
(If, however, you asked earlier and were refused, but now they offer it, you have a reason to suspect your manager's credibility - unless he can give you a very plausible explanation.)
Frankly, a good manager should have let you know during these two years that your contributions are valued, and that they would like you to stay. But not all managers are that good. Without knowing any details about your actual work environment, project, team & manager, we can't really advise you on whether to trust him or not. But if you have serious reasons to quit, which can't be alleviated by some more money or shinier title, then the best thing is to move on indeed.