Why can't I UV Unwrap this model like this? Extreme stretching First time here at Blender exchange.





So this is how I marked the seams in this test model but when I go to UV unwrap it this is what I get:



Its like regardless of what I do this part here never gets separated into its own island and I dont know why:



I'm obviously not an expert but I've UV unwrapped other models in the past and never had this problem, I've tried different things but so far I haven't been able to pin point the problem, so I'm sure I'm just doing something incredibly silly.

Any help? Thank you!

EDIT: Okay so I just found that I had a couple of vertices really close together and they seemed like they were one so there was some edges that werent marked as seam! But, now that I've fixed this when I UV unwrap it even though it's a lot better I still have this:


Why is it stretching like that there?

EDIT 2: 

EDIT 3: What I'm really trying to understand here is that in this example:

Why are those vertices appearing in the wrong position, and why if I manually try to move them in the correct position the other vertices in the other island get moved too even though they are in a different island?
The problem lies in the ngons so you have two options here.

a: Select each faces you want to have an island of and unwrap/smart unwrap it. This won't attach both side as one island but it will give you consistent uv maps for both sides. The UV islands will be overlapping so you want to pack the island.


b: get rid of the ngons: 
it looks a bit botched because I knife cut the faces in a hurry.

edit:
You might want to change the method and check/uncheck fill holes to your liking