| Hey, I had the same problem some time ago, and it really was annoying. I had picked up Coran and Yeslick at the Cloakwood forest, and I wanted to visit Beregost first, before cleaning the mine, to deliver the wyvern heads. First Yeslick gave a warning, after about 5 days, that he wants to go back to drown the mine. Then after 5 days more, he left my party, inmeditately joined, left it, joined it etc. etc. Very annoying.
So what I did was, that I loaded a previous game and waited as long as possible with him giving me the first warning. You can do that, just by giving him orders all the time, so that he can't walk up to you to complain. Then, at the entrance of the mine, I let him give the warning, which gave me 5 days untill he would give the second warning so I could easily clear the mine, without giving him direct orders all the time.
Though you could also decide just to drop him off somewhere, and clearing the mines without him, if that's okay with you. Just make sure that you still have a save game where he wasn't going all nutty yet, so that you can always back-up on that one, in case things doesn't work out. You never know.
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