Should I stay or should I leave?

I have been together with my boyfriend of 3 and half years, and I would like the relationship to move forward and take a next step. We are still not officially living together, even though he sleeps over at my house every night. He now tells me that he has doubts about our relationship, that he is not sure he is ready to commit to move in together or take a next step. At the same time he tells me he is also not ready to leave the relationship, that he loves me very much and wants to make out relationship work. I feel this limbo is what ultimately creates a sense of unease for me, I never know where I stand in his life, and I allow it to become exhausting for me mentally.