Letting go of someone's past?

My boyfriend and i have been dating for about a year now. When we first started dating he was into pot and he even sold it for like 2 months. For a little while I overlooked it because I was in the "honeymoon stage" where it was very hard for me to see any flaw in my man, but as time went on, I asked him to stop and even broke up with him for a little bit because I was doubting my feelings for him. Now, I have no doubts I love this boy with all my heart and he loves me just as much. He stopped smoking/selling and even drinking almost. He said he did it for himself and he's never been happier in his life. I just have the hardest time letting go of the person he was when I first met him, not the person he is growing into. I'm in college so I know I'm still young and inexperienced with serious relationships, but I want to spend the rest of my life with this boy and truly give him my whole heart, but I can't do that without coming to terms with the past. I understand weed isn't even that bad and is legal is other parts of the country, but I'm still not okay with it. How do I come to terms that my boyfriend used to be a "pothead"?