Split his shares in two?

While not in a business, here's my experience:

When I was young, I rented a house with what I thought were good friends. One friend wanted to bring his gf. We were friends, so I said sure. Turns out, both couples alienated me beyond my comprehension. They weren't mean, I just didn't exist as they tended to each other.

One couple I stayed friends with, the second didn't fare so well.

The moral of my story is that the dynamics will change, and you are the odd one out. Best of luck!