Behind everything
Up until the very last second, Alex had been wondering whether it was the right thing to give himself up. After all, in a way everyone in the tenth family had been dragged into a fight to protect him.
Would they forgive him, once they found out? Would they blame him for being selfish having made this decision on his own?
Would they understand what he was thinking at the time? Perhaps sympathising with how scared he was allowing that strange vampire to take him away from his friends and family, unaware whether he would see them ever again?
Ultimately, the reason why he had decided to go along with the powerful vampire was because he didn't want Logan to get hurt. Or anyone else for that matter. Before the vampire had entered the facility they stood a good chance, but after witnessing what he had done to Borden, he knew that even if Logan and him teamed up it would be useless.