Why did you stay? That was so stupid, you had an out. Everyone was weak, everyone was resting. He told you to run, run as fast as you can, and yet you didn't. You stood right in front of him and didn't waver once, simply staying with him until he regained his strength and wound up feeding from you.
When you told him you stayed because you loved him, he vanished. He was angry, in disbelief. Not at you, no, never at you. He was angry that he had let you fall for him, someone so violent, so dangerous. He was about to snap. The idea of punching walls got more appealing by the second. He was nearly blinded by anger, by fear, and by something else he refused to acknowledge.
Your arms wrapped around him, and in seconds, he was calm. You knew where he retreated, knew where he hid, and you found him rather easily. He made a feeble attempt to discourage you from comforting and loving on him, but you stood strong. He's stuck with you, and while he can't admit it to himself, he's ecstatic about it.