My boyfriend doesn't feel the same about me, how do I know when it's time to break up?

My boyfriend has been with me for 3 months, and things have been wonderful. it's the healthiest relationship of my life, and i really want, and see, a future for us. I'm willing to do anything for him, and I love him- and he's told me he loves me too. But, he's also had a couple times where he's been cold and distant because he isn't sure what he wants. Now he says he's happy with me but sometimes he just wants to be alone. It's becoming clear that he doesn't feel the same about me. I thought he was the one. What should I do?