>>82814681 (OP)
You think this is a fetish, it's not, it's what every man wants
Breaking up with big sis is not a thing
She knows everything about you from birth and loves you at some baseline level
She might make actual demands of you that is not standard transactionary subcucked 'hehe i'm just a gorl' foid nest hopping
There's none of the gay power dynamics issues either since the guy becomes taller and larger than her and requires a prospective change but the background history remains the same
People think next door childhood friend scenario is the ideal but by all the relevant metrics of judgement, big sis love scenario would always come up higher.