I don't know what I feel. But I do feel there's alot to this whole sad situation....more than what will be said I fear.
Like ... Motive?
It's not just about his mom. There's more..
I think he is seriously ****ed up in head, putting it bluntly! I think he is as messed up and sick as he is evil.
I think there are issues connected to abandonment, with him being bought up by his grandmother, then seeing his own mother taking on someone else's child.
I think there is an issue with his interest in teenage girls, which only would become a problem as he got older, and the gap between ages would make it illegal.
The hoarding is a sign of mental illness, and the hoarding on lesser scale at Becky's house (but which wouldn't take much to escalate) is relevant too, as either its his stuff so is encroaching into their space, or it belongs to another member of Becky's family, meaning another hoarder/person with mental health issues.
With his mum's illness, and Becky's mental health issues, I think that family was full of stresses.
I think he is also very immature and hasn't actually grown up himself yet - going by his obsession/jealousy of a 16 year old getting more attention than him.
What SH adds to that mix, I don't know. However, from what Retribution was saying before he/she left the thread, I got the impression there is more we don't know about the family, which may also have contributed.