One way of looking at Breaking Bad is with Walt posited as The Devil and Jesse as the poor sap who's battling for his very soul. With that in mind it becomes very clear that Walter White does not like it if anyone gets close to his partner. In Walt's twisted reality Jesse belongs to him and only him and he'll be damned if anyone is going to take him away. Remember when the love of Jesse's life started to overdose in front of Walt? Remember what Walt did to help? That's right, Walt did nothing. He just stood by and allowed it to happen. Not only was this an act of control but also because deep down Walt didn't want Jane getting in the way of his master plan in which Jesse was an integral cog. Then there was the budding relationship between Jesse and Gustavo that turned Walt a nasty shade of green. We don't need to tell you how that one ended. Jesse and Mike were close - Mike ends up dead. Everyone who means anything to Jesse sooner or later finds their way onto Heisenberg's radar and things don't end well for them. Arguments could even be made that Walt's sole motivation comes from his jealousy of his former business partners at Grey Matter who found nothing but success once he was no longer associated with them. Whether that's true or not we'll let you decide but one thing is for sure Walter White is a very jealous man, and that does not bode well for anybody.
