Adventure 390 (Mar/April 1970) is an 80 page giant that reprints 5 stories from her run in Action Comics. I will be talking about those individual stories when I cover Action, but I included this to highlight how much of a romance comic the Supergirl series was in the 60s and 70s.
This issue has stories of two of her main boyfriends from this era, Dick Malverne, who she met while in the orphanage, and later went to high school with. He was essentially her `Lois Lane`, in that many of the tales had him trying to prove she was Supergirl.
Two of the stories in this issue deal with her romance with Comet, the Super-Horse. Somehow the bestiality element never seemed to occur to the writers.
This issue also reprints the tale in which Supergirl finds an alien double of herself, and matchmakes the woman and Superman.
From bestiality to quasi-incest, the path of true love never did run smooth for Supergirl.