In the dawning of that awkward moment of realisation of the obvious, that in his panic Alek missed basic vital information of Carla's location, another decision was made. Even more rash then the last.
Alek moved with all his might, he cared not for secrets right now not that anyone should be able to make him.

In seconds he would be back by the tree he only just left, Sabine still nearby would be easy to track. He would be upon her like a flash.
With every remaining ounce of inhumane strength and speed Alek would surrender to the beast he so desperately and consistently fought hard to suppress. Charging Sabine into the nearest toilet cubicle (Preferably an empty handicapped)  he would sink his fangs into her flesh as he relentlessly bites her and ravages the fresh blood from deep within her veins. Gorging on her sustenance. 

To reach Carla and fight of an assassin vampire Alek needed more sustenance and vitae quick.
He couldn't risk or bring himself to attacking a human, not while there were still other options anyway.

Hopefully Sabine would understand, Alek didn't have time for explanations. He didn't even have time to consider what he was doing.