What do you do when loving someone hurts you?

You love someone for a very long time.
They claim to love you… BUT..they refuse to commit to you. They are there constantly, and intensely with you and for you for patches of time, then disappear, randomly, and without explanation, only to pop up again once you’ve accepted their absence. Spending more time with them only makes you hurt more when they are gone…but of course you don’t want to lose them from your life. What do you do?!?!?!