So to draw this crystal I used the pen tool for the outline and used line segments for the inside lines. Then I joined all the line segment anchors. I was left with two paths: the outline, and the inside lines.
I would prefer to draw this so the entire shape is made from one path. Is there a better way I can draw it to achieve this, or is there a way to combine the two paths into one? I can’t seem to do it with the pen tool without it wanting to delete anchors when I just want to connect the lines.
There is no, sane, way you can make this into one path!* Nor do you really want to either.
Group it and it will behave like a one object. Select all lines and hit Ctrl + G.
This kind of thinking happens to beginners. They realize that there is no need for an underlying modelling system to model reality the same way as you perceive it**. There is a benefit of thinking of lets say a coffee cup being 2 objects (handle and cup) fused together. In fact it’s impossible to model anything sane if everything has to always be done in one piece.
* A line simply can not branch. Yes, that means that there is a totally insane way of doing this.
** Nothing says your perception is correct. Being able to move in your thinking between different abstraction levels flexibly is a critical skill in the modern world.