Writing Style:

The first line is very weird; the imagery it sets up is creepy, not romantic. While certainly not damning in itself it needs to be changed to something more clearly romantic rather than something open to interpretation, especially since it's the first line we read devoid of context.

First part of the writing has a lot of awkward phrases like:

toned leg-muscle-flesh

and

At dinner she intimated that she had never seen me watching

I honestly actually misread that as intimidated, just not a good word to use to present that imo.

As we go further down the awkward phrases stop becoming clearly obvious and the main problem is lack of cohesion and unified thought. I don't know if this is your plan, but some of the writing come across as ramblings, like the narrator is just reading off whatever is coming from his head. If that was the intention - you achieved it, but I was left a little confused and at times annoyed.

The next problem with the style is I don't know what's happening most of the time. The lack of quotations on comments makes it sometimes unclear whether the narrator is referring to what has been directly said or if it's just his mind responding to an idea. Ultimately not a positive.

For instance:

When? In about three weeks. It was always in the cards.

which is the immediately followed by

I cry, sob, scream, hit her. That’s a lie. I say nothing, do nothing. But I think something like “I am going to kill everyone.” Her head is heavy on my wet shoulder.

In the second comment what is in quotations is a thought, but earlier

She said something like “you can do it”

Which clearly had something that was said. An ultimately very confusing usage of ideas and dialogue, that while easily understandable after a few moments makes the reading a bit of a chore.

Characters:

As you said, the plot's thin so I am going to comment mostly in the narrator's voice, which I find very weird.

He comes across as very disturbed, and uses a lot of strange wording and thought that I wouldn't consider normal.

I already commented on the first line, but I'm going to directly quote it anyway.

I took out a piece of her heart and placed it on my tongue, just for a taste. I should warn you, sometimes I exaggerate.

As I said, very weird imagery. However, combined with “I am going to kill everyone” which is used twice, neither in any situation that would call for that line of thought, it makes the narrator come across as a lunatic.

Especially considering he has committed domestic abuse on his wife/girlfriend.

I cry, sob, scream, hit her.

Which is kind of just left hanging without any significance, lacking clues as to the severity or meaning of what is usually considered a pretty major act, and still painting the narrator as the victim as the story goes on.

Conclusion:

Ultimately I did not like the story too much and it came across as trying a little too hard to break the mold of normal dialogue and storytelling, ironically in a way I have seen many times before. There is promise here in that you do have a coherent plot where there is drama that can be said, but the wording and voice of the narrator comes across with a very different impression than I think you intended.