There we go, now Junpei is finally on board with the revelation that his own gf Rumi was cheating on him with his scumbag fuckboy of a "friend". But man... he forgave his lying and cheating gf? Damn. Big mistake, should've broken up and found a better girl. There's no "It was just one time" in my book; once a cheater, always a cheater.
Also, it would leave a bad taste in my mouth if Touko suddenly bails on the plan, after this manga made a point of showing she was committed to revenge in the earlier chapters. She's not gonna dip, is she? That would ruin her character. I hope it's just Yuu being flaky as usual.