I started by drawing a 45° wedge (lazy, I know)... I had an idea of making the lines interweave and thought, "that shouldn't be too complicated to do in Illustrator..." (I was wrong, lol).

So in Illustrator, using a brush I started by tracing over just half of the original sketch, then I mirrored the image and joined the paths. Then in the appearance panel, I created a line style by creating a 5 pt stroke in black and then a 3 pt white stroke over it. Then I expanded the strokes (to separate the 2 strokes) and outlined.

That was the easy part.

The hard/intricate/time consuming part was copying and pastings parts of the lines, then using the pathfinder to trim.

Here is the finished piece. I really liked it, reminded me of lace.

Then I added some color. Also, I thought the center of the image looked a little plain so I added more detail.

Here it is as a pattern...