Change
Telling you a tale of an individual. He is mediocre. Not in a sad way but in a self-aware way. This individual in a way believed he was incapable of being loved. Time passed and to his delight and luck, he was proven wrong. He was taught how it felt to be loved. He was shown what it means to love. He never wanted to lose this person for the person was (and is) the best thing that ever happened to him.
Cut a while later, the two of them encountered numerous challenges. They sailed through the turbulent winds from compromises and patience. But this person came to realise that he was not able to return the same kind of happiness his favourite person gave him. He messed up. He hurt her on more occasions than one. He felt like to her he was a liability. To her, he was a disappointment.
He wanted to change (he still does) for he wants to be by her side and wants to make her happy. He wants to be a person she is proud she is dating. In this process, he learned something. (Caution: it's a little philosophical) It's more important to unlearn things in life than to learn. He has some terrible habits and traits that's pushing away his favourite person. He learned he has to be a better person. A person for whom she wouldn't be settling.
From unnamed sources due to a confidentiality agreement, we got to know that he is extremely apologetic. And he wants to make for hurting her and jeopardising so many things.