Strange line behavior at intersection

Something strange is happening at this intersection. I’m not able to select a line where it seems to be on the drawing space, but if I highlight it around it, it’s fine. I’m just trying to extend and trim these lines so they’ll meet (or alternatively move the black one (in this image, yellow) onto the white one, but it’s not letting me select the end point of the line, only the end point of the control points (it’s a straight line so I’m not sure why that’s there).

Can you upload a .3dm file containing the lines? It’s difficult to? You can use the vertical arrow above where you type a post.