Wiring Type: 3-way with dumb/existing switch
So of the three diagrams relating to this wiring type, I believe this is the one that applies to my setup: 
I just wanted to get a better idea of the swapped black wire. Since in my wiring, the black is connected to a bunch with the red nut. For context, there is a group of neutrals blocked by the switch to the left. Or am I getting my wiring confused with the wrong diagram?
To get started, you’re going to need to post better pictures. For the box that you already posted, pull the black bundle with the red cap out so that you can clearly see all the conductors and trace them. Also post a picture of the back of that switch so that I can see the connections.
You will need to post pictures of the other box as well. You cannot accurately assess a topology without looking at both boxes.
Thanks for the quick response Bry, For now, the only other picture I have is of the back of the switch in question.
This is the back of the other switch
This was from my attempt to install several days ago, so everything is put back together, but I hope this provides at least some information. The other switch contains the same three colour wires, with no neutrals in the box. I will get back to you with the other pictures when I get the chance to open it back up again.
Thanks in advance.
Unfortunately those pictures are not very helpful. As @Bry mentioned, we’ll need to be able to see all of the wires inside the box and where they are going (what bundles are they attached to, etc) for both boxes to be helpful here. While there are normal conventions for the colors of the wires, not everyone follows them well so we can’t give good advice if we can’t see what the wires are actually doing.