I hate to admit it, but there is some truth to what Risako said "No matter how many times you try to build something on a rocky foundation, it's only bound to collapse again" this isn't even about the yuri anymore, what would be best for Kaoru right now would probably be to divorce Reiichi and start anew, I mean did he ever truly love her? or was it just him holding himself accountable and feeling guilty about it all these years? I see how it would give both parties some form of security at first, but how is something so destructive supposed to work in the long run?
But if she really wants to start anew with Reiichi again then the both of them need to seek some sort of advice and fix that long-lasting "responsibility" problem, otherwise it might just ruin their relationship even more, and once that's solved, then they can try and build a relationship again, but that's only if both parties are willing to commit to one another and create a healthy relationship together, but again, with everything that's going on right now It's easier said than done.
Either that or she can get with Uta instead and maybe we'll finally get that long-awaited Yuri ( ͡° ͜ʖ ͡°)