In both sub and dom non-ntr routes, you will eventually replace Darian without being cucked.   

In the non-ntr sub route, you can choose replacing or sharing

In the non-ntr dom route, you can choose replacing, sharing, or netori (you're the bull).

In the ntr sub route, you are the cuck. You will share, but always as the sub.

In the ntr dom route, you'll go from the cucked to the cucker. Otherwise it's the same as the Dom Non-ntr route.