My Warden and Leliana were a thing for most of my canon playthrough... I think I cheated on her with Isabella though... might have been before we were official though... either way, she never found out. 
Nevertheless, we's was tight, but in the end I had to agree with Alistair, letting the old god's soul live in Morrigan's child would bite us on the butt one day, so when it was crunch time, I took one for the team. Ultimate Sacrifice. If I may say so, I thought that was a beautiful end to my Warden's story, first she lost her family (human noble), then found true love, but even though Leliana was waiting, I couldn't let Alistair shaft the crown I got him. The safety and longevity of the nation comes before one's self, such is the mark of any noble warrior.
In the end I recall something about Leliana went back to Orlais(?) I think, and wrote a song inspired by her broken heart. I hope this story is reflected in Inquisition. It will be surreal getting to know Leliana as a new character, and have her tell of her lost love.