Hell no.
the fact that stories about women who cheat or are forced to cheat & somehow suddenly find themselves nymphomaniacs doesn't mean it'd happen in real life... that's the typical male response to living in homes where women make most of the decisions, ESPECIALLY when it's acceptable to have sex... the entire reason Bram Stoker's 'Dracula' was & remains a well read novel & often imitated cinematic delight...
what's to gain in 'sharing' anyway? your wife finds out someone has skills/ equipment you don't, to your detriment, decides two at once is better even if others skills/ equipment aren't 'better' or doesn't like it & wonders thereafter if your real goal was to get her to 'share' you with her girlfriend... no winning scenario there...
a buddy did have a 3some as the 'added cock' in college... he said the boyfriend suddenly changed his mind in mid 'sharing' & then was peeved that his girlfriend wanted to keep going, trying to take it out on my buddy. & i don't imagine that's a particularly fun situation to find yourself trying to defend yourself or beat a hasty retreat.
so while Jeff Foxworthy is right... getting married for sex is like buying a jumbo jet for free peanuts... I'm not interested in sharing what i've got. i'll just look at the pictures of the sexy young things prancing around starkers & reading stories about women discovering the 'pleasure they've been missing' thank you very much!