Thighs Wide Open (2000)

After three years of marriage, John and Nikki Young are in a rut. Nikki is border line frigid and John has all but given up on her, when Nikki is slipped an invitation to a private party by a stranger she goes against her nature and decides to attend. Once there Nikki is exposed to an erotic world she never would have imagined. It's not until later that she discovers that not only did her husband know about the party, but he set it up for her. But interestingly enough she's not mad... she's grateful... and it looks like now they might just live happily ever after, after all.