Betrayal of trust.. ya think?

I haven't dated much and I have never broken up with anyone. Because I am new to this scene, I was hoping for a little wisdom for you. I dated someone for the longest I ever have- 1 yr and 9 months. I need help understanding what happened: How can someone say that they love you and they want to grow old with you and they want to marry, you, and they get your ring size, ask how you want to be asked to marry them and tell you they are sure that you the one, and then change their minds? I moved 1,500 miles to be with him and he told me he wants me to move on with my life and maybe we will get back together, but it won't be for a long time. I am actually asking, how can a person contribute to a relationship sincerely and then decide to basically betray the person's trust, pull out and break up with someone?