First chapter bares faults
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"It was a lie"
Needs punctuation; a period or a semicolon.
"I was planning on seeking out of here..."
Seeking or sneaking out?
“Yeah[,] and you should..."
"Cheating bastard could he just move out already."
Needs punctuation, e.g.:
Cheating bastard! Could he just move out already?
"Why did shit always have to happen to me!"
This sure looks like a question. Try terminating with '?'
"I suppose a part of me wanted to know why he did it, why he killed them. But I knew deep down why he did it; it was for me."
"He would have tracked me down, and killed me."
"...I roared, getting off the bed and walked to the door..."
Mixed tenses. Try:
"I roared. Getting off the bed, I walked to the door"
Also, if Scarlett is really angry, does she merely walk to the door, or does she storm or stomp or otherwise move in a plainly angry fashion?
"Nathanial Chambers was standing there..."
Yeah. We know his full name. You just told us. Maybe now he can be 'Chambers' (or the more familiar 'Nathaniel') or simply 'He.' There are no other males around. 'He' works.
“Um[.] sure come in.” I stepped back, letting him in to my room. “What are you[.] um[,] doing here again?”
“I wanted to see how you were going.”
“I wanted to see how you were doing.”
"In the mid of the attack at the pharmacy I hadn’t even taken notice of his physically appearance..."
"During the attack at the pharmacy, I hadn’t noticed his physically appearance..."
"During the chaos at the pharmacy..."
Bound all instances of "um" with commas. Consider discarding them.
“I’m so sorry[,] Nathanial, for all of this.”
“But we both know if I didn’t[,] you wouldn’t be here right now.”
Also, it sounds as though he had little choice but to take the shot in defense of Scarlett's life. It seems to me, having read only this far, that he should be less apologetic about killing a killer, e.g.:
"It wasn’t your fault, I had to take that shot." ... "We both know..."
“My lawyer told me [I'm not] allowed to see you.”
"I’m trained it’s my profession I knew when I killed them what I was getting into.”
Punctuation is your friend. Try:
"I’m a trained professional. I knew what I was getting into when I killed them.”
“Though those men were the first ones I’ve ever taken out without orders."
“Those were the first men I’ve ever taken out without orders."
“So you are a trained[,] what[,] assassin?”
...or exorcize the 'what'
"... ruining your life[,] but now ..."
“Here I was thinking you were having a bad reaction to finding out about my day job.”
“Here, I was worried that you would have a bad reaction to finding out about my day job.”
Also, 'have a bad reaction' feels weak. People don't generally 'react' well to paid killers. Maybe 'hate me' or something along that line.
"The police were waiting on my statement and once I gave it I will be confirming their claims."
"The police were waiting for my statement, and, once given, it will confirm their suspicions."
“You know[,] for a good looking girl[,] you worry too much.”
I'm getting tired of pointing out all the missing commas. From here I'm going to do the most prominent cases.
It's OK or okay.
"He looked aimless around my room."
Try 'aimlessly', or "He scanned my room."
"He asked not sounding to interest but just trying to remake some conversation."
I think you mean "too interested"
“But you have [to].”
"This isn’t your problem[,] which is [what] I came here to tell you."
I only read about halfway through the first chapter, just after Scarlett "stormed up the stairs."
This is starting to look like an interesting tale, and I will read further as I'm interested to see where it goes, but you need to work on your punctuation, especially your commas.
Also, I'm not a enthused about Scarlett's attitudes about herself, e.g., "I knew my life wasn’t worth saving." This is sprinkled all over. Why should we care about someone tho thinks she's worthless?