
I don't think so. Both of them are hiding secrets from each other, and she's aware of it (at least in the novel she is).
I think what she means is that he'd literally do something against her or her family, like the second prince and his faction have done until now. But we all know Dean would never betray her like that ╮( ̄▽ ̄)╭

Starting from there, Iris never inquired further into his family. The main reason she actually trusted him was because of how capable he was and because her own family said good things about them. If you remember the first time they met, he asked her not to go in further and she complied saying that "she didn't need to, as long as he didn't betray her and did his work properly". So right from the start both knew each other had secrets but they were fine as long as they worked fine together.
She said she couldn’t take it if he ended up betraying her now, is him lying about his identity a betrayal as well?