RW,
You asked for a little Simon, so I hope you take this in the spirit of anonymous internet criticism in which it is given.
A few thoughts I had reading the longer excerpt:
First, the great first sentence debate. You gave a very lengthy explanation in a previous post about how the literal leitmotif for the character of Capt. Jonathan Bluff is also literally the leitmotif of Jaime, the narrator. But it isn't. Does the music blare out every time he enters a meeting at work? Or gets mad after opening the cable bill? No. It's still just the theme music for his character. However, the narrator might *feel* like it's literally his (Jaime's) leitmotif, which is different than it actually being, (Saying it's "his" in the sense that it's his character's and the character and its associations belong to him is splitting hairs.) It still exists in the realm of the poetic, and therefore conflicts with the overtly factual, removed tone of "my ex-girlfriend" in the latter half of the sentence.
I might have done something like: "Captain Bluff's leitmotif - my leitmotif, as it drags me onto the stage of consciousness - wails out of Chelsea's TV. She always watches this sh*t in surround sound". I will say, the lack of poetry in the second sentence is an *effective* use of tonal contrast to underscore the character's feelings.
As for the "ex-girlfriend" part, that information can wait, even if it's just a couple of pages later. Maybe a moment when he's looking in the bathroom mirror and wonders why he's sleeping over at his ex-girlfriend's the night before her wedding, giving us more info on his state of mind. You're writing a novel. You can take your time in doling out info to the reader. As one of my writing instructors once said, you have to allow yourself "a sense of play" when writing, especially with a longer work. You do provide other small details without being to authorial to let us know what's going on: mentioning the rehearsal, the fiancé. All spread out a bit and letting the reader piece it together from a more "natural" train of narrator thought.
Second, do you realize how much of that section you gave us is devoted to what's going on in an animated show the characters are watching rather than what's going on with the characters themselves? A lot. A whole lot. Made me want to put on my "Don't tell me about your character!" T-shirt. Plus, there's a tone issue: first the narrator calls what's on the TV "sh*t", then goes on to describe everything in exacting detail. He's obviously somewhat uninterested, then even uncomfortable watching it. Why is he then so invested in explaining, even "in his head", what's going on to the reader? He's not. It's you, the author, that wants to describe everything going on in the show. Is it really relevant? We only need Jaime to give us his synopsis of each scene, preferably colored by his current state of mind. And more importantly, keep giving us information about how he and Chelsea are reacting to what's happening.
Also somewhat distracting was Jaime describing the action on the screen in the first person. Yes, I know when people talk about what their characters have done in a game, they often use "I", but sometimes the natural way of speaking can make for lousy story-telling on paper. There's added awkwardness with phrases like "the real me", "back on screen", etc. since he's also describing what's going on in the living room. He's watching a show recreating the exploits of a character he plays, not himself. In fact, since the machinima is created by someone else, narrative control is no longer his. It's perfectly fine (and less confusing) for Jaime to refer to Captain Bluff as "him" while passively watching. (I realize that perhaps you might be planning on playing with issues of separation of identity - is the character you create and play "you"? If you are going down that road, saving Jaime's reference to Bluff as "I" for when that separation starts to blur might be more effective.)
If the exact events of the machinima are important to the story, you might reconsider the method in which this additional narrative is conveyed. Having Jaime watch and simply tell us what's going on in each episode would get quite tedious. Perhaps giving each chapter a prologue consisting of the only Fleet action Jaime described, but done in third person, or first person, where the "I" is actually Captain Bluff. Imagine starting that first chapter off that way, telling us all the action in the Fleet story first, *then* revealing that it's all some sort of video piece based on a game he plays. Also, opportunities for juxtaposition of events for effect open themselves up.
Lastly, tied to the second point, I don't have much of a sense of place. Take time to give us more detail about the real world, too. For example, "I’ve carved out a nice warm patch on the living room floor". Nice word choice. But since he didn't literally carve a spot out of the floor itself, I'm getting the impression that there's enough stuff on the floor that he had to make a space to sleep. Is Chelsea a slob? Is it the remnants of a party, or the sleeping bags and blankets of other house guests? Where they up all night drinking together? The details can be informative about the characters or situation, or throw-away. Just let us look around a bit. Slow down. Have a sense of play. The other bits of real-world character description you do have are actually pretty solid. I just wish there was more of it.