Jaye and Mallory have endings, both single and a combined one (but not as a regular throuple). Mallory also has an ending with Amanda. Other girls from the game are set to feature in the epilogues as well, in what I guess might be called an "others" ending, or multiple endings. These are still to come, so we don't know the exact dynamics yet.
The next game is not a sequel, but it does feature two (that we know of) girls from this game - Tara and Lisa.
As for the question about harem, no, not for this game at least.