There are three words no man ever wants to hear come out of the mouth of a girl they've been planning to leave.
"She was glorious when we met. I remember distinctly the way the crazy orange of the sunset reflected in her gray eyes, giving them an otherworldly tint that somehow managed to make her perfect smile all the more beautiful. I'd been walking the dock, bored, looking for nothing in particular, when I heard her laugh harmonize with the waves, and looked up to see the most incredibly gorgeous girl I had ever seen smiling at me with her toes in the water. Boom. Lust at first sight.
She stayed beautiful for the rest of the evening, and then for the rest of the night. I'm not generally a second date kind of guy, but for her? Hell, I'd stick around. Days turned to weeks turned to months, et cetera. You know how it goes. Never thought I'd wind up in any kind of long-term relationship, but hey. Sex is sex, and steady is steady.
Thing is, over time, she got… Eh, I'll call it clingy. Yeah, Yeah, I know, that's to be expected. Sure. Like I said, I'm just not the kind of guy who's comfortable with that. She'd get suspicious, almost threatening. I'd come home late, and "baby, where have you been?", every time, like she wanted to catch me at something. Started asking my friends questions, too. Not cool.
Here's an example. One night, I go to Angelo's, help him set up the gallery for his next show. Took us a little longer then we expected, maybe half an hour. No big deal. I get home, she's on my couch, gray eyes brimming with tears. Now, I suppose I should explain- She didn't live with me. No sir. To this day I have no fuckin' clue how she got in there, but there she was, looking at me with those big pretty eyes. "Baby, you never called. Where were you?"
Before I can even answer, my phone rings, and it's Angelo. "Yo, how'd your girl get my number, huh? I told you, if you gotta' have people callin' me, give 'em the gallery number." I just hung up. She'd called him while I was driving home. It wasn't long after that that Angelo stopped answering my calls. Fickle bastard.
So, I start thinking about getting out. I've been tied down too long, yanno? And that's when it happens. Three words, unexpected, cutting right to the primal quick.
It was a normal enough night. I'd been working at a local movie theater for change, and stopped to flirt with the new ticket girl, and one thing led to another led to I'm headed home late. So it goes. Shit, don't look at me like that. Can't a man have a life? I don't tell you how to run your personal shit.
Anyway, I walk in, and the first thing I see is a broken glass near the door. Cheap wine all over the floor. Weird. So I walk cautious and loud, making damn sure whoever it is knows I'm home, and I'm a fuckin' big guy. And there she is.
She's leaning up against the kitchen counter, smiling, like she's glad to see me. And she looks up at me with those big yellow eyes, and says three words that damn near stop my heart."
…
"You should run."

...

Doctor Sander sighed and clicked off the portable recorder on his desk. "All right, D-1254. That's enough for now. Go on back to your dormitory." He motioned to the guards at the door, and they moved swiftly to escort the man in the orange jumpsuit out of the small office.
With another resigned sigh, Sander pulled a fresh memo from a pad and began to write.

SCP-3701-E victim designated D-1254, convicted of two counts of murder, one Angelo Dimuccio, 32-year-old male, one Toni Williams, 27-year-old female. He doesn't seem to remember doing the male, and from the sound of it, he didn't even think the girl was human at the time. Some kind of monster, trying to kill him.
The effect seems to extend to memory as well as perception. He doesn't recall his hallucinations as such, nor does he question the likelihood of their events. Beyond that, no lasting effect of SCP-3701-E has manifested, and D-1254 will be terminated at the end of the month as per normal protocols.
This is the fourth victim of 3701-E in two months. I'm recommending research into the cause of the hallucinations and delusions be made a Keter level priority, at least until we can figure out what it is and contain it.

Sander added the memo to a growing pile on his desk and rubbed his temples, then got up to go for coffee.