I’m a cuck for my big sis

I’m a 18m Cuck, I’ve been this way for almost 3 years now, It all started when my friends use to “joke” about wanting to fuck my big sis…It got so bad that I developed an addiction and spend all night, every night, in my bed jerking off while imagining my big sis getting a train ran on her by several men, all while I can’t do anything but watch since I’m too much of a pussy to actually fight…