Hmm, I am like that your friend, once someone close to me becomes successful, I leave, unless the person showed me that he still values the friendship.
You won't blame him, probably experience made him thought everyone that gets to the top deserves to be left alone. Some people who get successful act funny to their friends who are still trying to come up.
But I wish he understand you are not like that, you making effort to call or texts proved you really cared about him and will always be his friend regardless your class.
Thank you sir.