So the romance system is pretty flexible at first but gets more complicated as you go deeper into the story. You can definitely flirt around with different companions early on, but most of them will want you to choose eventually. I've found that shadowheart, astarion and karlach are actually pretty cool with sharing if you bring halsin into the mix, which is kinda interesting to see play out. Gale and wyll though, they're strictly one-person types from what I've seen.

If youre trying to juggle multiple relationships, just know that the game treats them as separate things rather than actual group dynamics, and most companions will make you pick sides later on. Something worth noting, those side flings with characters like mizora or the drow twins usually dont cause drama with your main romance. From my experience though, its best to settle on one main romance by the time you reach act 2s end, unless youre specifically going for that halsin-approved arrangement, since trying to keep multiple romances going can lock you out of some really good character moments.