Certainly the emotion and the character of Jennifer were stand-out points in this story - quite enjoyed it overall there. She made for a quite interesting deranged character and I felt sorry for the poor man who had been caught up in the whole affair without much of a clue for a good while of it. The structure was neat too with the way it lead up to each other at the end (particular with the two kisses contrasting each other), although I had been initially confused by what was happening exactly with the time skips back and forth in the first few instances - perhaps they could have been a bit clearer. In addition the ending was a little bit short/rushed for my liking, and feel it could have a touch more work on it. At times I felt the description was a bit overdone as well or rather the description of her love drove in a bit too much - perhaps intentional but it seemed to be a bit over the top for myself in a couple of instances - maybe just my personal taste though.
The prompt was used well though with it being the basis of the story, and overall I quite enjoyed the whole plot. Favourite moment for me would have been him saying that he did not love her - the sort of silence that followed in my mind when reading was quite a neat moment.
Her strained eye with its red, pulsating veins shining unhealthily through its sclera scanned her limited field of vision erratically, any semblance of order quickly proving non-existent. She hadn't slept in days, she was too uneasy.
I'll admit I had to go look up 'sclera' and it seemed somewhat an unnecessary way to describe her eye seeing I had never heard of it and hence felt that it was a bit too technical or obscure a term to use. At times I was a bit uncomfortable with how you split sentences as well with commas as it didn't sound *quite* right or could have imo been written slightly better, such as with the last sentence there - maybe a hyphen in place of the comma would suit it better instance, or rewording to ''...in days for she was too uneasy' or the like.
His smile, his posture, his oddly professional clothes, his hair, his body, everything seemed perfect, he was flawless.
This felt a bit too run-on for my liking as well - I feel it sounds better if the comma after body was changed to an ellipse or hyphen and the last three words made into its own sentence.
The man smiled and on her insides turned to butter.
The 'on' seemed unnecessary.
Almost every few weeks after he had left (abandoned!) her, he had returned to this very same spot across the street with a different woman, sometimes even a man!
Maybe add in an 'and' before 'sometimes'.
The only solace she took from his frequent philandering was that each and every person he saw would eventually feel the very same dejection she had felt when he had cast her aside.
Nitpicky but maybe 'cast her aside' could be 'cast them aside' given in the above quote she mentioned 'sometimes a man!'. I did like that the previous bit btw was the first hint he may not have been necessarily cheating.
"It's been too long –I've missed you so much.
The hyphen seems somewhat oddly positioned to me there, or a space missing.
Jennifer snapped out of her trance, he was addressing her.
Feel it's better as two sentences rather than one here.
Through the grime, it gleamed and caught her face in its light, its reflection revealing a strained, reddish eye
And again I'm not sure that 'through the grime' ends the comma after it but I can see it working both ways.
The light burned her, it rejected her unnatural presence, and she too felt intense displeasure at leaving her shelter, but something important needed to be done.
Run-on sentence here the way I read it - separating into separate sentences at least once (say at 'burned her/it rejected...') would help imo.
She stepped out of the house with the knife held loosely in her hand, the warm sun of spring casting its harsh glare upon her waxy skin that hadn't seen the light of day in ages. The light burned her, it rejected her unnatural presence, and she too felt intense displeasure at leaving her shelter, but something important needed to be done. She could no longer wait for him to reciprocate her feelings. She would no longer remain one of his plaything, cast aside deep in the bowels of his amorous memory banks. She would become his present and future, not just a blip in his past.
Four sentences in a row started with 'She ___' there which felt too repetitive to me - I'd suggest changing one or two of those sentences' beginnings.
Fatigue gripped her body, she had not left the house or walked this far in so long, and the cafe seemed so far away.
I feel a semi-colon works better than a comma after 'body'.
He searched frantically through the databases of his mind for anyone he had me in the past who would do this, any irate ex-girlfriends, any over-enthusiastic encounter in a motel somewhere.
Sounds odd around there - I'd say replacing the bolded bit with 'knew'/'met'/etc would fix it.
He retreated backwards slowly, taking calculated steps away from Jennifer and towards what hoped of as the safety of the counter.
Same as above - maybe try replacing with 'he hoped was'?
"My lovely darling bastard," she crooned." I love you, and you love me, you see.
The quotation mark after crooned is slightly mis-positioned.
She brought the knife down in a flash second,
'flash second' sounds odd to me although maybe it is just another term for 'split second' which I haven't heard of before (google didn't help me with confirming that...) - if so then ignore, if not then just 'second' would do imo, or split second.
Nice work overall - certainly an engrossing tale!