Petulia (1968)

When she sees him at a hospital fund-raiser, newlywed San Francisco socialite Petulia Danner, who has been married to naval engineer David Danner for six months, seems determined to have an affair with soon to be divorced physician Dr. Archie Bollen, who has been married to his wife Polo for close to ten years, their marriage which many saw as being perfect. Archie doesn't even know Petulia's name, but only knows her as the woman who brought in a young Mexican boy into the hospital with serious injuries. Petulia's pursuit of Archie is relentless - she even declaring that they will someday be married - even as Archie dates another woman named May. Archie eventually learns part of the reason why Petulia is so determined to cheat on David as her relationship to David and David's wealthy father are brought to light. Archie also learns that getting involved with Petulia in any regard has its consequences, both for Petulia herself and for him, most specifically in his relationship to Polo.