@cybik not necessarily if you are married to multiple people that would be more along the lines of polygamy or polyamory rather then cheating as long as they are aware you are married to multiple people.
Considering what she did and how much damage was caused to Tempest it always bugs how it handles her punishment. Without spoilers for the main story I know the reason Rimuru gives but doesn’t seem right after seeing how much sadness was caused by her.
Well most of the damage was done by farmus she only disabled magic spells so that they can't communicate to the outside world . rimuru knew that so instead of killing her he put her under arrest and if she really was a traitor she would have tried to run and not protect youm . The food and treatment that she is getting is the decision made by townspeople not rimuru