at the risk of sounding too 'sex and the city', all proper theatrical productions have an understudy in case of unexpected outbreaks of mono, crabs or a pimple. my personal comedy (ok, drama), involves a selection of such understudies, sans the over ventilated, toothy, julia roberts perma-grin.
appropriate criteria for the "if neither one of us are married 5 years from RIGHT NOW, then let's plan on shoving cake in each other's mouths and faces" are typically dictated by the ones with uteruses dessicating to the size of a sunmaid raisin.
understudies tend to be somewhat asexual, where the 'hotness' quotient is superceded by sperm with super powered flagellums. toe curling is not a priority when you are selecting from the 'i cant read the top letter at the opticians so i can overlook your hooked nose' donor list. understudies are fraternal. finally, all those horny guy friends who are "just like [my] brother" get their opportunity. they are bestowed the privelege of seeing the 'one week out of the month knickers'; all month. these are the guys for whom you will leave (already leave) the bathroom door yawning when constipated for more accessible requests of last months 'people' magazine, or when the sphincter is so dilated that another roll of TP is of immediate medical necessity.
essentially, the long term personal ad requires someone who would be willing to wipe my bum when im 84.