Folks, cheating is going against previously set up rules. Tetra and Almus already talked about this in 36.1, Tetra set up two rules (second marriage = OK, breaking family = not OK), and Almus agreed with this.
In the context (see 35.2) it's clear what she meant by "breaking the family": marry one of those girls who were flirting with him. It's unclear if she's against solely political marriages, the Dibel family, or even Almus marrying someone she doesn't know and/or respect, but guess what. Yuria* is someone she knows and respect, she is not from the Dibel family, and Almus actually likes her. It's fine. It is not cheating, period.
*It's a bit too late for that, but her name is clearly Latin "Iulia". All three have Latin names (Almus=kind, Iulia=young, Tetra=shocking. Yeah... poor Tetra got the short end of the stick here.)