How do I stand up for my wife over something that happened months ago?

Long story short, back when my wife and I were dating there were a few times crap went down between her and her friends or her and my family and I never stood up for her. Its nothing Im proud of and for the most part I always took it as problems that would just blow over. But she never got over the fact that I didnt stand up for her and its always bothered her. She lost trust and respect towards me because I didnt speak up or take sides. A few months ago we were separated and someone commented on one of my fb pictures and referenced her looks. Later on when we got back together someone told her about the comments and she flipped. I had forgotten about them entirely because I didnt see them as important. But I shouldnt have let ANYONE say anything negative about her ever. I know this. There are no excuses. But how do I fix this now? Do I bring it up to the people who i really dont talk to anymore just to try and get her some closure or what? We were on a really good track and and then this pretty much gouged open her old wounds. Shes hurt and doesnt want to talk to me because she feels betrayed. What do I do? And how do i fix this?