You say "please only contact me when there is something urgent, I'm quite busy and don't always have time to reply nor do I feel right about not doing so, so please respect my request. I will do the same for you" ...just thinking out loud! By multi texting over and over to you he is not respecting your space or your status, it's almost like he's keeping his turf staked. How do you keep someone out of your head when they are texting you continually often for no real reason? He's making it difficult for you to move on.
