Since the events that recreated him as he now is, Cloud has never been alone, even in his own skin. Between Jenova, Sephiroth, Zack, the Lifestream's tangled whispers, he fears his existence owes more to them than him. He doubts where he fits, whether his soul has room left for him, or if he'd recognize the real Cloud on meeting him.
When Tifa shows him the truth in the Lifestream, Cloud understands finally that he was only ever real in one moment. When he died killing Sephiroth, for his family, friends and everything he loved, that's where Cloud is.