Words on a yuri manga: Wagamama Juliet volume 1
Wagamama Juliet (Selfish Juliet) is a two-volume manga by Iizuka Shuko. It ran in Young Rose (a josei manga magazine) in 1994. It's out of print, but you should still be able to find it used. The ISBNs are 4049280590 and 4049280604.

The story bears some resemblance to Moonlight Flowers (which ran in a similar magazine, Office You, in 1989-1990), with the lead (Youko) getting married despite the fact that she still loves an old classmate (Ayari) from junior high, one she is reunited with just before the wedding. But the villain in this one is Ayari's boyfriend--he's clearly a jerk, an abuser, and a cheater, and when Ayari blabs to him about Youko's feelings for her, he decides to use that information to get money from Youko and her husband. When Ayari leaves him (after being roughed up and having him force himself on her), refusing to participate in the scheme (and telling Youko as much when she crashes at Youko's place), he goes to Youko's husband, Kouta, instead. He says he'll tell everyone that Youko is gay unless Kouta gives him a huge sum of money and kicks Ayari out of his apartment.

Youko knows that she is gay, but, not having ever met another gay person, she feels all alone; that's why she decided to date and marry Kouta--to try to be happy as his wife, even though she doesn't love him and always feels like crying after they have sex. She feels guilty about what she is doing, but thinks she can make things work with Kouta. Until, that is, his little chat with Ayari's ex. Youko and Kouta decide to try and save their marriage anyway (Kouta goes so far as to say he wants to "cure" Youko's lesbianism, which rubs her the wrong way), but there is friction between them, with each of them hurting the other despite their good intentions.

Throughout volume 1, Ayari has been saying that she doesn't return Youko's feelings, even claiming that she wouldn't sleep with her if they were the last two people on the planet (it's established early on that Ayari is a cruel person, far from perfect, and yet Youko loves her anyway). But at the end of the volume, she reveals that--gasp!--she is in love with Youko. The two spend the night at Ayari's new apartment.

Will Kouta become a secondary villain, or will he remain the well-intentioned but somewhat clueless husband? I guess we'll find out in volume 2.