Neal knows that there's no such thing as originiality. Every art movement had its predecessors; every genius had their inspiration. Every con has been done before, usually in a plethora of variations. Every brilliantly innovative risotto or cocktail, at some point, is based on another.
So there is no great shame in being a far better forger than he is an artist. But truthfully (so to speak), Neal does think he's a great artist. "Neal Caffrey" is his best work to date.
An identity is exactly that. It's not just a name, it's a person. He's a little bit in love with "Neal," honestly, even though no persona has ever gotten him into quite as much trouble. From the start, he wanted Neal to be a gentle soul, to be his one identity that didn't try to project toughness to other criminals, who got by on brilliance and brilliance alone. He's childlike in some ways, looking to others for approval and guidance, his weaknesses ranged from silly to heartbreaking (he always made sure his identities had weaknesses - no one could become a perfect man). Neal wasn't afraid to love too much or too fast, and for a man who spent his life guarding his heart like a sword in an iron box, it was liberating to be Neal, to be open and giving. To be unafraid of joy and greatness, and to demand it, even. Slowly, he turned "Neal Caffrey" into the kind of man he always wanted to be, the man he could have been if life had turned out just a little bit differently, the kind who pursued challenges instead of avoiding them, the kind who chose loyalty over safety or money or anything else. He knew that he could never be a Neal Caffrey who didn't make mistakes (no one could, but especially not him). But in his (many) other identities, including his real one, he had done too many things for the wrong reasons, and he decided that as Neal, he would do it for the right reasons. For people, for beauty, for thrills, for his own (rather avant garde) sense of morality, but especially for love. After all, if he had known all along that it's never worth it to put anything else above love, then he might not have had to become someone else in the first place. He used Neal to bring out his very best qualities, the person inside of him that he desperately hoped was always there. And it was - it just went by the name of Neal.
Even on the days when Neal had gotten him into something he thought he might never get out of, it was Neal who saved him from it. On the days when he felt he would never be able to get out of bed, he would say to himself "Neal would be resilient enough to get through this" or "Neal would never let them get away with this" or "Neal would stop crying and stand up and make a plan." Even when it was Peter who saved him, he was still saved by Neal in a sense. He knew that Peter could never be as close to any of his other personae as he was to Neal - Neal, who compulsively showed off his talent instead of hoarding it like a secret weapon, who wore his heart on his sleeve and his wit on the tip of his tongue. Whose worst qualities made him more like a teenager acting out than the type of man he was before he became Neal.
Leaving June and her family would be hard. El and Diana and Jones would be hard.
Leaving Peter was going to make him hate himself. Especially since he knew Peter would take it personally, would think of it as a betrayal rather than a continuation of their game.
But leaving Neal Caffrey behind was going to be the hardest part. He didn't want to think about the kind of man he was going to become without him.