He does take care of the baby and raises him like a son. He shows his mother and she believes it is his and won't believe it's not. Later the boy grows up and he's bi, he has a threesome with his girl and guy friend all the time, but he likes his 'father'. The father starts to suspect the son is gay, but isn't sure. Then at school the son gets caught with the girl, before the other guy came and so the father assumes he's straight. He tells the son, "I'm so glad you're normal, I was worried for a while you were gay"(or something), and the son takes it really hard. That's pretty much where it last left off, but I forgot to save it, does anyone know what it's called?

Papa's Assasin. - Ryuunosuke wa Tonde Yuku.