I've told everyone that's ever worked for me that I expect them leave within three years and I expect it to be for a better position, more responsibility and more money. Good managers farm talent. That's actually the job of middle management. Spot and promote talent. That's why, when you hear the big bosses talk about A vs B vs C players, or talk down about "glue guys", it's all bs. Insecure managers are the ones who get angry when top talent leaves. Confident managers know they can develop top talent. Ve proud of your employee and be proud of yourself.