How can I love God when I can't see him?
The short answer
What you know, you can love, as you can love Mother Teresa without having met her. You know far more about God than you realize: a crucifix shows more love than anything else, and everything you know is evidence of his love. You were made for loving him.
You can love God, just as you can love Mother Teresa. You probably know more about her than about many people you deal with daily, and what you know, you can love.
You know far more about God than you realize. Look at a crucifix: you will find more love there than anywhere else, and learn more about his love for you than about anyone else's, however well you think you know them. Everything you know is evidence of God's love. You are well prepared to love him; everything about you was designed for it. It is why you exist.