Yes, you will meet the girls again in the disco and can explain to them whatever you chose to do before.
Well, the game encourages you to get involved with Triss and Charlotte, but you don't have to.
About the tags: It's a rule here not to put up tags for "promised" content, meaning: So far there is no harem way in the game.
It might come at some point, but so far all routes are basically solo or in the best/worst case involve one more girl as side character.
Completely solo ... I think that might be possible if it's possible to avoid getting in bed with the boss. I have to try that, see how much of the story is left