Desir says in chapter 1 that many friends and lovers were lost. Emphasis on the plural. Later when he meets Romantica, he does not say she was his lover, he simply says he fell into despair when she died for a while. They could've been lovers or very close friends.
I don't know what it says in the novel. I tried to read it and match it up but it was a machine translation so the best I can tell, when he met Romantica in the past he didn't say anything about her death in the future past.