Inescapable (2005)

College friends and ex lovers, Beth and Susan plan a long awaited reunion in Oregon with current loves Chloe and Jessie, who are instantly attracted to each other upon first meeting. While Susan and Beth attend daytime conferences, their partners are left alone with very little to do. They try to suppress their feelings but it's only a matter of time before passion explodes and they embark upon a torrid sultry affair enticing the lovers to take bigger risks with increasingly reckless consequences.