I'm looking for a word that describes Person A in the following situation:
Person A pretends to be friends with Person B but when B goes off to start a business, A secretly doesn't want B to succeed (possibly because A feels that only he should succeed and feels threatened by the success of others.)
"Narcissistic" could work but doesn't capture the insecurity of the person. "Jealous" and "envious" suggest that there is already some achievement to speak of. Similarly, being a "hater" typically implies that the hated person is already successful.