Saw this movie on cable (Showtime or Cinemax I think) in the late 1980s / early 1990s.  I believe the movie is originally from the 1970s, possibly the 1960s, judging by the music and clothing / hair styles.

It starts out with a young couple getting married.  I think the ceremony and/or the reception was outdoors.  That night they have sex.  It’s a long, dimly lit scene, where they start out having a playful pillow fight in their bedroom, and things progress from there.

But ultimately this isn’t a movie about a happy marriage between two newlyweds, but one of the wife cheating on the husband a number of times, and her dealing with it.  There’s a scene or scenes where she’s confessing to an older / grey-haired psychologist guy.  I think she also has a female confidant who she confides in.

Early on (I think this was the first time she strays), she notices a boat outside her and her husband’s lake house (or maybe they’re on an island?), with a mysterious stranger on the boat.  It’s driving her crazy – she wants to know who this guy is.  She’s pacing back and forth, asking herself “Who’s on that boat?” and psyching herself up to find out with affirmations like “I want to experience!” and “I want it all!”  Then it cuts to a hot scene on the boat where they’re going at it on the bow.  I have a poor quality clip of that scene uploaded on a NSFW site that I can include later if that’s ok.  That scene is later replayed in flashbacks when she’s confiding in her psychologist and/or friend.

She has another encounter with a biker looking guy in a cinema.  They’re sitting beside each other, when he starts playing with her under her dress.  Later in the movie she participates in an orgy – I think the biker looking guy brings her there.

That’s all I really remember.  I don’t remember how the movie ends, whether the husband finds out about her infidelity, etc.

This movie was in color, and has a European feel to it.  It was in English (as I distinctly remember the “Who’s on that boat?” and “I want it all!” lines), although it might have been dubbed.

Any ideas?