He said I was perfect for him, but he chose someone else?

This is one of the most difficult things to have to hear. Someone tells you one thing that gives you so much hope and then turns around and does the opposite and takes it away. Unfortunately this is a common occurrence. Oftentimes people will say things that sound good in the moment or will say things to diffuse tensions and avoid any sort of conflicts. The important lesson that can be learned from this is that people often will speak louder with their actions than their words. Remember always that your value is not determined by this person and that the idea of a perfect person is impossible to meet because it is so subjective.

Sometimes it is the right person, but the wrong time. Sometimes they are just not ready to be in a committed relationship with somebody that they know will last a long time. Either way, they decided that they were not ready for whatever reason. I know some people don't want to be with the person they feel is perfect for them because they are afraid of not being good enough for them. Not having enough money, relationship experience, life experience, a steady job, emotion control skills etc. Maybe they think they have some growing to do and don't want to risk completely ruining their chances at a serious relationship with you or maybe they have commitment issues.