He says that his sister was the first person he told years before he got the courage to come out of the closet, she always supported him. He's only 2 years older that she maybe because this they were always very close. The sex between them started when his sister got her heart broken by a stupid guy. First the long talks, then the sleeping over, the laughs and finally the sex. It didn't happen over night maybe that's the reason he doesn't want it to end.