Here are a couple of examples that suggest that it’s possible to love someone without knowing whether or not they exist. The first is from Alexander Pruss, the second is from Andrew Cullison.
1. Fred is lost in the desert and dies. Without knowing this, Sally, his loving wife who is a presentist and thinks there is no afterlife spends weeks searching for Fred in the desert, in uncertainty whether Fred is still alive, despite great hardship and danger to her own life.
Observe that a presentist who disbelieves in an afterlife thinks that the dead are simply nonexistent. So Sally is not only uncertain whether Fred is alive, but she is uncertain whether Fred exists. Yet she acts out of love. Hence:
- It is possible to love someone while being unsure whether he exists.
2. Bob is lonely and begins a chat-room relationship with Julie. Bob and Julie are both grieving the loss of a loved one. Julie offers words of encouragement that no one has been able to offer Bob. Bob does the same for Julie. Then Bob’s friend Steve provides Bob with an overwhelming amount of evidence that Chat Rooms have very sophisticated Turing Machine Like programs that can perfectly replicate close, personal conversation with other humans. Bob is nervous. It is highly likely that Julie is a fake. He stops believing that Julie exists. He even tells Julie that he doesn’t believe she exists. However, he holds out strong hope that Julie exists. He says, you may not be real, but there is some very slim possibility that you are – that’s enough for me to think this is worth continuing. Eventually, they meet. They marry. Someone asks them ‘When did your personal relationship begin?’ Bob says, ‘Back when I didn’t even believe Julie existed.’
These examples are suggestive and have obvious implications for the atheistic argument from divine hiddenness. A key assumption in that argument is that knowledge of God’s existence is a prerequisite for loving God. Insofar as these examples make us question that intuition, they weaken the force of the argument from hiddenness.
dude ex machina 
Good effort, but i would not say these are the best examples. Being unsure of something that does not exist, and having a relationship with someone you are not sure exist. Are two entirely different things. (And for obvious reasons also weird. )
I’ll grant you that the two examples are different. If we make the assumption that Fred is dead and thus non-existent, the two cases aren’t really parallel because in the second example, Julie does exist. We could modify the first story to make it parallel, i.e. Fred survives but is lost and Sally is unsure whether or not he exists.