He shouldn't have let her in
She was a traumatised orphan with dangerous people potentially after her. Could've drawn police attention aswell straight to his door. He exposes his trade to her and takes on hits for her sake with no payment to show for it. Spends time training her without any understanding that he will earn anything from her hits.
It turns out LATER that she gave his life meaning but that was just a lucky coincidence. He didn't look for company and also made it very clear in the very beginning that she can't stay. He ended up getting killed because of her.