Wait for the Month 1 merge, and it should be two, assuming you want the Dark Mind patch.
Hard to say, but Kotori getting in on the action and/or Mao's parentage coming to light will be the key factor of getting her on board.
A few pages back, someone suggested that perhaps Mao is actually the MCs daughter, after he lost control and raped her. In this situation, withholding the information is to prevent him from breaking from the guilt. Even if this isn't the case, I very much doubt she willingly cheated. It seems obvious to me that she was raped and that it was too dangerous for the MC to go after who ever did it. Perhaps, I'm way off base, but the MC getting cheated on feels antithetical to the kind of story Ecchi Sensei is.
That would require he Month 1 merge to get pushed to get pushed back to about February if their release schedule up until that start is anything to go by. So far, we don't have any indication that the release won't be when they say. We don't have any that it will release on time either, but tthat doesn't mean we should be jumping to conclusions. Latecomer explained why they don't work on things side by side about month back. Can't remember what was said, so you'll have to go searching for it.
She's been popping up a bit more frequently lately, but mostly as comic relief. I think the Dark Mind dev is still intending to include content with her at some point though.