I would talk to you about the concept of the scip.
about how something that clones people combines tropes of doppelgängers and copy machines in an unoriginal way, but how SCP-XXXX needs to know their name and face like he's Light Yagami is kind of a cool twist
But the concept isn't the point. This is meant to capture the experience of being a sapient, humanoid scip. So I'll focus on the aspect of writing that will drive this home: Character.
It sounds weird at first thought, but you need more pornstars and fewer dead siblings/parents.
The part I felt humanized SCP-XXXX the most was the mention that he used his power to fulfill his basic sexual needs, which is perfectly normal. Many of us would try desperately to take care of that business while in containment, and humanoid scips feel all that more un-relatable when they don't. On the other hand, having a dark and troubled past where all of his family is dead makes him more like every other superhero than like any of us. Killing off all familial ties he might have on outside cuts off another contact point between him and the reader that you could explore.
In a similar vein, his weight gain also adds to his character (literally and figuratively). It seems like a mundane point, but it actually reminds the reader that it's a person – a human being who, like every other human being, can get fat – the Foundation has put in a cell. I advocated for the removal of this detail from the description, but I believe it belongs in this article. You've done well here.
As I read him, Damian Sabio solely serves the role of "the friendly guy MC kills because MC can't control their powers." Perhaps this is the only role he can serve here, but I'd at least try to flesh him out as more than that.
I think I like your characterization of Stephanie Rom the most. You've nailed the apathy she brings to the table with SCP-XXXX – the "I just work here" attitude, the type of attitude that gets threatened by normal people in anomalous circumstances. It's clear she's uncomfortable about getting close to him, and that discomfort betrays the sliver of sympathy she has for him.
On one final note: I'm really glad they didn't hook up. It's a natural consequence that they'd part; otherwise, it would be artificial in an un-pretty way. It's poignant allegory that no matter how normal the person is, their anomaly will make them inhuman.