Boyfriend and his girl best friend

My boyfriend has this girl who he's been best friends with since middle school. I'm currently pregnant with his child and am starting to realize I don't think we have the same relationship he has with her. I love my boyfriend. He's great and funny and ambitious but in starting to wonder if I truly know him like she does. My boyfriend used to be extremely addicted to pills and other hard drugs. She was there for him when he ended up comatose because of an OD and through rehab. She knows a lot about his life and what led him to doing drugs and things that happened when he was on drugs. I know about his addiction but he prefers not to talk about that time in his life because it was hard. He was face timing with her and asking her why she stuck around and by his side. He's been going through this thing recently where he's been thinking about how badly he treated the people in his life when he was own drugs and apologizing to a lot of people even though they already forgave him but he was crying talking to her asking why she stuck around because he treated her like shit. And her reason was she knew he was a good person deep down and just struggling. I'm just wondering can our relationship be as strong? I just feel like our relationship is second base compared to there's