Except they aren't really glossing over it at all. It comes up on almost every second page, it's the crisis point of the story and it's the subject of the very last sentence in the manga so far. In fact, it's been the reason why Ishida and Yano have stayed separate for years despite sharing such an obvious passion for each other. So, I don't know why you say it's been glossed over.
Please revisit chapter 3 and witness what I'm talking about. He even tells Yano not to give up on him and there is not even a thought saying "what about my wife and kid?". There is no such thing. He goes and cheats without thinking. It took him some time before he even realised he had an affair. The majority of voices is saying "he can deal with that later" or "why can't you be happy for them?"; all reason out of the window. Anyway a this is MY opinion and you see it with your own view. To be honest I detest cheaters- they are selfish and don't think of others.
like how they gloss over the fact that he had an affair... Plus he has a KID!! （￣へ￣）