Can't think of any songs directly about same-sex relationships, but there are certainly traditional songs which hint at attraction between members of the same sex or more often than not, via that handiest of plot devices, members of the opposite sex dressed up.

Two examples that spring to mind are the Female Drummer, who's found out by a young girl who falls in love with her (the song doesn't state exactly how she finds out), and The Famous Flower of Serving Men, where the King is "beguiled" by his serving man (who of course is really a woman)

There's also Willie o' Winsbury, whose beauty gets him off the hook when Janet's father admits he'd be his bedfellow too (if he was a woman of course, which he's not)