I am beginning a new game of BG2. I want to pursue a romance with Aerie and also have Haer'dalis along. The problem is I've heard that he falls in love Aerie himself, resulting in a sequence of events whereby either he or Aerie leave the party. Is there any way to avoid this? Cheat codes or Shadowkeeper? (I would need exact instructions.)

The Aerie / HD romance is not destined to end in either leaving (via a dual). What you need to be aware of is that if your character and Aerie's romance reaches the point where she asks if you love her first, she will choose you (assuming you say "yes") -- HD loses; she will tell him and he will stay. If HD reaches the "do you love me" stage first, Aerie won't give him an answer until she's spoken to your character ("do you love me?"). At that stage it's up to you how it turns out.

By the way, is there any mod that disable romances completely? I can't stand them any more.

Then don't get involved. Simple.

That's not enough. At the worst possible moment, somebody initiates a stupid dialogue.

So? Turn them down. Piss them off. Dismiss them from the party. Do what the hell you want. You don't have to have a romance if you don't want one. If you make it plain right from the beginning that you're not interested it will end quickly. I don't see the problem.

That doesn't prevent the dialog from initiating in the first place, so it doesn't actually solve gunman_'s problem.

(I actually wouldn't mind a mod that disables *all* banter, and makes it so that quests only start when the player initiates them.)

Why am I not surprised?