Since the two of you have broken up, and she’s looking to move on, I think you should take your cue from her, and move on. The social media photos mean less than her behavior. And she could have just not gotten around to replacing them, or they might not be as important to her as they feel to you. I know you want her back, but after three years and a clear break up, the best thing you can do is move on. Whether or not she’s dating someone from her past or not is no longer your business. You’ll be a lot happier when you start dating someone else, and you’ll be less focused on her, and more on your future.
As for friendship, let it go. It’s not really a friendship, anyway. Why? First of all, men and women can’t be friends. One reason is that there’s always an undercurrent of chemistry, romance or some other dating desire — if not from both people, then at least one. This isn’t the basis of friendship — it’s romance. Or lust! Second, it’s impossible to be truly honest and happy for each other. For instance, a true friend would be excited for her that she’s meeting with these new guys — but because you’ve still got romantic feelings for her, you’re acting like an ex-boyfriend, not a true friend. 😉 A friend would have been happy that the guy she dated in 11th grade reached out to her! You weren’t. 😕 And if she felt that you were truly a friend, she wouldn’t be so secretive about this other “friend” she’s seeing.
I know it’s disturbing to have to move on after three years, but it’s going to be the best thing for you.