Join paths pen

I'm trying to join two paths with the pen tool. The shape is a coffe mug, took me half an hour to try to combine paths with the pen tool.

I'm trying to join where the little white gap is. I had the same issue opposite but I managed to draw a little curve in there and join the paths. But I can't seem to do it the other side and I don't understand how it works.

I attache a pic and a movie.