I'm at 19 reputation and any neutral character in my party I speak to immediately leave. I tried reinstalling the happy patch but it doesn't work. Any idea what's going on?

Sounds like you are playing a modified version of the game; neutral characters, while they may complain if you reputation gets to high, will not actually leave in the unmodified version.

Therefore, the issue is likely in one of the mods you are using, or in the way they interact with each other.

Posting a list of the mods you installed and the order you installed them in might help someone more knowledgeable answer this question. (If you are using WeiDU, there's apparently a way to get the log; posting that might help.)

Yep it's modded with :

- Baldur's Gate II Fixpack
- BGT-WeiDU
- Baldur's Gate 1 Unfinished Business as well as BG 2 Unfinished Business
- widescreen mod
- Setup-BGTMusic.exe
- Baldur's Gate II Tweak Pack

I've looked in the doc but can't find what could be causing it. The happy patch from the tweak pack wasn't installed, I only tried it after having the issue. I'll try to get a log like you said, thanks.

According to this list, you shouldn't be able to speak to character in your party at all. Only they should be able to initiate dialogs.

Which characters are the ones leaving? Jaheira? And in which part of the game is that happening?

It's Safana, Branwen and Faldorn. It's true that up until now, when speaking to party members it would say "X has nothing to say to you". It still says that with Yeslick and Coran.

Maybe I should just not do that? Will some other trigger cause them to leave? I'm in chapter 6 after flooding the mines.

Branwen has a trigger on one of the states in her dialog file: "HappinessLT(Myself,0)". The trigger is present in vanilla BG1+TotSC. This trigger fires at reputation of 19 or 20 for a neutral character, which set "Happiness" to -80. This causes the "You are no more honorable than the Loki spawn I left behind." dialog to fire and Branwen to leave the party.

Faldorn and Safana have dialog states with the same trigger.

So, it's not a mod or a bug, it's just the way the BG1 dialog triggers were written.

Still, shouldbn't be leaving.
You can install happy patch (see tweaks anthology) to alleviate this.

If I'm not mistaken, mods only affect games that are started after the mod is installed. So belatedly installing the happy patch won't help this particular save file, though it might solve the issue for a new game.

astrobryguy thanks for the info.

I've kept all three, they complain once in a while but don't leave. I've rested and had other reputation gains, I think it'll be fine if I keep giving them the silent treatment.

Depends on the mod. Happy patch specifically will work in progress.