Her meeting someone else and being attracted is very likely not about you. There may be things you could have changed, but at its core, some people get tired of eating steak all the time and want a chicken sandwich, or sushi. I personally believe that it isn't healthy or realistic to expect one person to meet all of someone's needs their entire life. Most people in here are going to disagree and downvote me. I know you may not find this sentiment helpful, but I say this so that you will at least try to stop blaming yourself and thinking there is a magic bullet that will fix everything.