whats this manga called?

this manga is about a boy who is picked up by a man and starts to live with him (the man has a son). After some time the man dies and the boy and the son are the only ones left and theres a huge dept on the house. the boy has sex with one guy (i think he bought the house or was to collect the money) to pay fo the dept and all this time the sin of the man doesnt know anything untll the very end