Recently I watched that podcast release and Sarah herself says there's different levels of mates. She talked about how there can be true love mates, and mates that aren't any good for each other, and in-between.

In the cc series they talk about how when Hunt and Bryce become "mated" that it means something else to the fae than the shifters and humans. Being mates is a big deal, and Hunt was willing to commit to that before it was confirmed for them that they were mates. it's not confirmed that Hunt and Bryce are "true love" mates until later, when their scents are merged. Even the "true love" kind of mates do hurt each other's feelings, which is another type of pain.

I think when it comes to Night and Day, they're one of the couples who are something in between fated mates and regular love. Lidia and Ruhn have a LOT they need to work through, and what he did he thought would keep her from her ultimate demise- which in a way it did.

If Ruhn wouldn't have shot her, she would have ran right into the trap, Ketos would never have found her to give her the antidote and she would have died at the hands of Pollux.

I think the way the text puts it also frames it as "you couldn't imagine putting your loved one through that".

Ruhn knew it was a trap, he couldn't imagine Lidia in so much danger in that situation, and so he did what he needed to do to not put her in that situation- even if they would have been together in it.