Beswitching, I'm not right now going to nit pick all my way through this. There are plenty of little nitpicks I would happily make, but we'll come to them later. Oh, except for this one:

Quote Originally Posted by Beswitchingly Positive View Post
she started to quietly panic.
Split infinitive. Quietly to panic or to panic quietly.

Please don't take anything I say as insulting - it is truly intended to be constructive criticism and done with gusto, because I think your story is worth it. I really do like this story: as I said, it is chilling and compelling.

However, there are two main things that give me problems.

One is - too many short sentences. Try to mix and match a bit more. Now, I know that the narrator is breathless, enclosed, feels claustrophobic: so there are moments when this choppy style really suits the atmosphere. However, there is too much of it. Here is one example of a way in which you could tweak things, (which also sorts out a sentence that just seems to be sitting around on its own):

"All the neighborhood girls called him Papa - he had loads of young girlfriends."

The other issue you have is use of tenses. The story has a current narrative, in the past tense. But it also has background, and this is in the past within the context of the story. If you used your tenses to differentiate between these two phases, it would make it easier to read/understand. At the moment, you start with the pain in your chest: and then, all still in the same tense, you go back over the past; and we don't get back to the moment when the narrative began for a good number of paragraphs; but this isn't currently clear to the reader.

So:
"Pain grasped my chest as I started to walk away from Celia’s apartment. It was not the pain of heartbreak, more like almost drowning. She would not let me be. "

This is the story narrative.

"In the beginning, she was strong, calm and quiet. Back in the good days, we fucked every night. After I quit my job, she started to quietly panic. I could not breathe around her."

This is the story background. Try:

"In the beginning, she had been strong, calm and quiet. Back in the good days, we had fucked every night. But after I quit my job, she’d started quietly to panic. Gradually, I found I could not breathe around her."

Similarly, the old guy on the roof - this is not something that is happening within the current narrative, it is background to it. The summer heat becoming stifling also - it is stifling now, but it became stifling over a period of time, which is before the moment of the narrative.

Have a play with that stuff, and I'd then love to pick your next version to happy shreds!