Snow was highly secretive as an agent. Other than Aceras, the only few people who have seen her in person could be counted by fingers now.
Scratch that. Thousands have seen her and became aware of her identity, but she killed them off to preserve her confidentiality and further make her more invincible in her line of work.
Connections were troublesome for her. If she could live without Aceras' management, she would.
After all, it's not like she liked Aceras or anything.
To her, knowing and keeping someone by her side was akin to taking responsibility of them because of the highly dangerous career that she chose. Aceras was great at this line of work too, but that didn't exempt him from her treatment to anybody else.
The assassin Snow's rules were ironclad.
Cross them, and you will face the consequences.
Aceras hadn't crossed her once. That's why he was still allowed to be around her.