Okay, this guy is actually Peter van Daan. But he's a little bit like Peter Pan—he's mesmerizing, innocent, and more than a little reluctant to grow up.
It's not as though we blame Peter—whose actual name was Peter van Pels—for his immaturity. The situation he finds himself in is so horrific and claustrophobic that it makes sense that he'd prioritize getting through the days instead of bettering himself.
But Anne, with her characteristic wit and snark, doesn't really see it that way.
Through Anne’s eyes at the beginning of her diary, Peter is lazy and has a weak character. He’s also shy and extremely awkward, hardly a person worth her notice. But a year and a half after they’ve been in hiding, Anne suddenly starts to notice that Peter looks at her with longing. Soon she has a crush on him, and decides that he is very sweet and desperately in need of affection:
In the meantime, things are getting more and more wonderful here. I think, Kitty, that true love may be developing in the Annex. All those jokes about marrying Peter if we stayed here long enough weren’t so silly after all. Not that I’m thinking of marrying him, mind you. I don’t even know what he’ll be like when he grows up. Or if we’ll even love each other enough to get married. (3/22/1944.2)
But Anne is soon disappointed with Peter—making this teenage romance totally similar to so many others. He doesn’t like religion and he is too lazy and weak to improve himself. He seems satisfied with mediocrity and takes the easy path in life rather than one of work and personal growth. He also either isn’t as deep as she wanted him to be or he doesn’t know how to open himself up to her. Anne also realizes that the romance was a byproduct of loneliness:
I know very well that he was my conquest, and not the other way around. I created an image of him in my mind, pictured him as a quiet, sweet, sensitive boy badly in need of friendship and love! I needed to pour out my heart to a living person. I wanted a friend who would help me find my way again. I accomplished what I set out to do and drew him, slowly but surely, toward me. When I finally got him to be my friend, it automatically developed into an intimacy that, when I think about it now, seems outrageous. (7/15/1944.9)
Peter promises Anne he will never fight with her, because neither one of them wants things to get uncomfortable if they fight and then have to continue living together. He doesn’t fight with her, but it is never clear if that’s because he’s keeping his promise or he just doesn’t have any fight in him. It's not that he is a peacemaker—he's just a passive guy.