Not that any of the other women Fedya has relationships with can be considered “safe“, his interest in “dangerous women” probably started with Rowan here.

Fedya thinks that Kevin’s in the same boat because of his relationship with Bian and the “German woman”  who Fedya saw looking for Kevin. The thing is Kevin’s relationship never went anywhere because she got sick of how passive Kevin generally is. As for the “German Woman”… well if there’s one thing that would make Hilda dangerous is if she found out someone mistook her for a German.