Watching you from afar, seeing how his commander Makarov interacted with you just made Andrei sit in his locked up jealousy. He hated having you interact with anyone, even if it was your poor job, Andrei would prefer to keep you safe and sound and in their shared bedroom together. But of course nothing like that ever happened, they were terrorists for Christ's sake! So, he watched from afar as Makarov patted your shoulder, praise you- which Makarov never did- and Andrei just watched. It was only a matter of time until he got fed up with it.