I made a little ramp, then next to it is a brush that goes up diagonally. The problem is that the face from the back part of the ramp gets deleted, and I don’t think it should do that. How can I avoid this?
We do know of some known issues with BSPs. That being said, you do want to stick to some rules with BSPs to help them out. Think in Quads (4 vertices) when you can and always weld vertices when you try to overlap them.
True some of those tips and see if that will help restore your ramp’s back.
The vertices information is more generally modelling information and from your new image I do not see the need to do that but in generating geometry try to stay away from triangles as whole pieces of geometry.