Question: I heard that Leliana commits suicide if she is in love with the Warden and he dies at the end of the game. Is this true?
It's implied if she is left unhardened, from the DA wiki
“Leliana remained in the royal court for a time, mourning. She poured her heart into a ballad that would eventually become known throughout Thedas. But after one performance, Leliana quietly vanished. Some say that the Maker came to her in a vision again that night. Smiling, tears in her eyes, she told a maid that she would see her love again at last.”
whereas a hardened Leliana
“Leliana remained in the royal court for a time, mourning. She poured her heart into a ballad that would eventually become known throughout Thedas. But after one performance, Leliana quietly vanished. Some claimed she returned to a life of adventure, while others said that she returned to Orlais to exact revenge on her enemies. Whichever is true, she never forgot the one she loved.”
I only did the ultimate sacrifice ending once, on my first ever run of DAO, I was a noob in those days. 