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If he thinks that you hang on his every word he may find it unattractive. Letting him know that you will talk to him when it suits you can build intrigue and show him that getting your attention will be a challenge that will be rewarded. Keep him on his toes and reward him for finally getting the chance to talk to you. It will make him value your limited interactions. Be careful not to blow him off too many times or he may think that you will easily to ditch out on him. Don’t reveal too much of yourself too soon.  Keep your interactions fun but brief so that he wants more and values your time.
Don’t answer his calls. Change your schedule. Establish intrigue to draw him closer.