It probably stings more because you opened yourself up with the letter to him.
As a guy, I dont know that I would feel comfortable writing a detailed letter to someone I like until I have at least rounded the bases a few times with them (which may happen this weekend).
You cant guess as to why he chose her and why she is changing her life and moving to be with him. Nor should you think of any things you could have done different that may have changed his decision.
One things is certain...you will get over this and move on and find someone else. There are a lot of single guys your age in Kansas. I do know that it is best to try and date someone who lives close to you.
