It sounds like he maybe likes being liked and isn't ready/unselfish enough to let you get on with your life without him. Not to say he's being horrible, just that perhaps he isn't yet able to let go. You need to decide, therefore, whether you want to move on without him or talk about the possibility of waiting for him.
Whichever you decide, if it were me, I would need to do it quickly in order to start finding peace. I wouldn't send him a letter, I would do it in person if you are going to do it. Because if you send a letter, your head will then likely move on to wishing for a reply and waiting for one. At least if you do it in person, you will get an immediate response and can move on.
I know what it's like to want desperately to make contact. I currently have thrown away the charger to my phone so I cannot text my exAB! My head says one thing, my heart says another.
A
Follow you head sweetie, it will look after you.