Hi, thanks for the questions!
The sharing content (if the player specifically chooses this route) involving men will be physical in nature only, and Valerie will not develop any emotions for them. From her perspective, these men would be nothing but an additional source of sexual energy: tools for her, in other words. This opens the doors for both regular scenes as well as content where she is much more dominant towards them, depending on the player's choices.
On the other hand, the open-harem route gives the option for Valerie to have both sexual and romantic relations with the other heroines (Rena and Annestria specifically), while forbidding her sex with anyone else. Note that you can also choose to keep it purely sexual between Val and Rena/Ann, in case you aren't interested in the polycule idea.
Finally, the monogamy route keeps it simple: Valerie is only ever interested in the MC, both sexually and romantically, period.