Did you skip through everything or read the actually story? Because it's pretty clear what happened to Miru and where she has gone to. Of course, the last update left off there and we don't know what happens next, but it's easy to figure out where she went.
There is no harem tag, so in general, there won't be a harem as far as I know. And as for you sleeping with another woman, that was your choice. You're not forced into it lol. In my playthrough I am completely faithful to Miru. If you slept with another woman, then that's on you.