John is experiencing his first true love with a woman, and wonders, “Don't you know it's going to last.” He is immersing himself in this love, and realizes he will do all he can on his end to make it last. Perhaps he mused for a moment that if his mother had loved him like Yoko did, maybe his fears and perspective on love would have been different. A sort of “What if” somebody had loved him like Yoko did? Maybe John was referring to his mother. “And if somebody loved me like she do me,” was probably a sudden thought John had. John acknowledges “Nobody ever loved me like she does.” It's the love he had longed for, and now that he had it, was afraid to lose it. He is ready to give up the Beatles and move forward with her in love, as artist, and activist. John Lennon echos a plea to Yoko that she must not “let him down.” John's love for her is so intense that he knows he'd be shattered if she left him.
