I'll toss in Design for Living - it is actually a poly film(!) from the 1930s(!!), with two guys who fall in love with the same women. They come up with a bargain where they can both have relationships with her as long as they don't have sex. Of course this fails hilariously; hijinx ensue.

The movie is great and, outside of the love triangle depicted, the two guys are slashy as heck.