Roshi was a child of a broken home. His Father left his mother and he was sold more than once for her drug habit until he was stolen away to become a prostitute.
[Which explains his knowledge of sex before Kain and the bruises and cuts that can be found on his body.]
He became the man prostitute and managed to get high salories that only pissed off the rest of boys who sold their bodies. He had regular beatings and was constantly stolen from. Sometimes tricked to willingly give money after falling in love with one of the boys, only to be teased and tortured for it later.
Running away, tear stained, bloody, and bruised, he ran away downtown passed Heaven Cafe where he found himself on Kain’s bar doorsteps. The day he met Kain was the day he also forgot everything but his body and heart still remembers the beatings and heartbreak he has grown up in having.