Rueben stops waiting in the garden for Eloy to reform after a while. They changed their identity to live a separate life and let "Rueben Cadel" finally die. Also to be able to further separate themself from their father's atrocities. They still visit the garden on the rare occasion but they've stopped waiting for Eloy after Astral grew older and stopped visiting.
Also, as I was looking for Rue's chapter to check their pronouns, I noticed that I made it cannon that Pandora is 27 years older than Seven and Sin- x.X
Suicidal-Prince
That's what Rueben looked like btw. The top picture. Not that outfit tho.