The other day I came across a title in IMDB called A Small Circle of Friends
, which a reviewer said addressed "menage a trois" tastefully. I think I might've seen it way back when, but not sure. Sounds like a good one to look up. Karen Allen was always so cute!
RfromRMC, not familiar with that movie you mentioned, but maybe searching keywords or asking at one of the boards over at IMDB.com might help you find it.