Break up with him.
Know that before both hearts can completely heal, he will be falling for someone else's lips, smiles, and the way she dresses. Maybe he will love her in a way he never did with you.
It will feel like you're going to die. You're out of breath, drowning in pain. But before long you will be doing the same thing. Falling for someone so fast. It will take your breath away.
One day, it will come to you that he probably forgot how you used to smile when he woke up next to you in the morning. You will know, because you're starting to forget the color of his eyes, too.
One day, it will take efforts to remember that you were, once, in love with this faceless person in some distant past.
That, is how you leave someone you love and break your own heart.