It does feel like a lot of set up for no payoff. The previous chapter took the abuse so seriously that the resolution being so clean feels like brushing it under the rag. Like, does the mangaka want to dive into the subject or not? They should make up their mind.
I think they may bring this up later, because as Suuna said, both of them haven't properly talked about their past. What we need to focus on is how Ruka has dealt with it and how the author didn't walk back her character development. Also as the crazy ex mentioned they weren't dating, she called herself a sefure, she never actually dated properly Ruka, and Ruka knows that and simply didn't give her the time of day, and that's what you can do with someone like her.
This topic will be brought up later, I believe, as they develop their romantic relationship deeper as a Romantic relationship, and not a sexual one. Which I also think is the contrast between this and Shino to Ren.