Some of the things you write seem to be not entirely true. Halsin isn't really forced onto you. You can kill him if you want as you write yourself, the game works just fine if you do.

Even if you have him in your camp, you do not have to have him in your party. I never took him along, so I never got the scene and dialogue between SH and him. If I'm not mistaken, you anyway would only get the scene for a foursome if you first ask for that yourself. If you shut down those drow from the start (or because seen from a PG POV, you are in a relationship as you say, maybe don't approach them at all, because it's clear they are prostitutes), you also wouldn't get that scene, even if you have Halsin in your party, or?

At that point of the story, Halsin's main part if over anyway, so even if you want a druid in your party, you can take Jaheira instead (who has more interactions in Act 3 anyway afaik).

If you romance SH, and you do not make a certain decision in the game to push her to wholly dedicate herself to someone else (but which is probably the most prior telegraphed plot point in the game, so no surprise there), she will not abandon you in the end. If I remember the ending correctly, it's the opposite, you kind of make plans what you'll do together after this is all over.

I also don't think it's ideal, but if you are bothered by it, you can avoid most of it.