|In the first place, losing your temper only generates problems for you. Although you apologized, this incident has probably cast you as the villain. At the same time, if an employee is withholding information in areas where you are in charge, a discussion is clearly warranted, whether such an employee has “forgotten” or not.|
Secondly, you should clearly take advantage of your manager’s offer to help. Frankly, he should already be involved in this matter. His role will not necessarily be to deal with your co-worker’s “forgetfulness,” but rather to investigate the situation and rebuild communication, collaboration, and trust in the department. Instead of regarding this matter as petty, it’s a central component of your manager’s job.
Whether this situation is based on jealousy, ostracism, or any other factors, the key step is to address it now. Left unchecked, you’ll end up packing your bags or even having them packed for you.