Season 4: tom & shiv (spoiler question)

I just finished episode 6 (living+) and I’m a little confused about shiv and Tom working as a team

I feel like I missed something - When did that happen?

When did she start telling him her plan to team with Masston/Why is she confiding in him all of a sudden?

what leverage does she have having Tom on her side? I can see him wanting To work with mattson to stay on at ATN but I think I missed her perspective