The girl, Minori, met up with Ruka @ that omega place. Then one day they noticed she stopped coming and it's found out that she's actually a married woman. Ruka is saddened by this because he felt a bit happy being with Minori and looked forward to seeing her once more. He ends up choosing the black haired dude and his mysterious personality leaves him wanting to get to know him better. He eventually finds out that he's Minori's husband and that he met up with Ruka because he wanted to get back at her in a way but he ended up a bit interested in Ruka. It's hard to tell how Ruka felt about this considering how he tends to always be positive. I guess he was used by the married couple (?) But for two entirely different reasons. Also in the extras, it's revealed that Minori met up with Ruka that one time because she wanted to use her front, in which she is unable to do so with her husband (I'm guessing that means he's an Alpha). I'm sure this probably doesn't matter to you anymore but I still wanted to try and explain
Thanks I really was confused, but you made it clearer.（＾ｖ＾）
The first story was sad, but I really hope the brother fine someone. (T⌓T)o(╥﹏╥)o
And for the second story, I'm not sure what happen. But I think the girl he was messing with knows the guy he chose. And I think they set him up probably? ╮(─▽─)╭＼(;´□｀)/ I'm not sure if I'm right.