To make things look interlinked, you have to use some tricks. What you're going to do is use an object and a clipped clone to make it look like a part of one object is going over and then under another one.

First, get your letters into their positions. I used different color letters to make it easier to see what's going on. I'm going to be working with the two Ds, and leave the B alone.

Identify the places where you want to see overlap. I've circled in red the three spots I'm going to do for this example.

Make a clone of the first object, in this case the left D. The clone is created on top of the object stack, but in the same location as the original D. So now we need to hide all of it except that spot we want to overlap. We do that by setting a clip path.

This blue rectangle will be our clip path. Where ever the blue rectangle and the D-clone overlap, the D-clone will show. So we need to make sure the rectangle completely covers the point where the D-clone and the B overlap. Making the blue rectangle 50% transparent helps with placement. When it's in position, select both the rectangle and the D-clone, and go to the Object menu, Clip -> Set.

Here's what it looks like.

Now clone the other D.

Make rectangles that cover the corners of the D-clone we want to show. This case is a bit different because we need both blue rectangles to be one object or the clip path won't work right. So they need to be grouped (
Ctrl+
G) first. Then select the rectangle-group and the D-clone, and go to the Object menu, Clip -> Set.

Here's the final result.