Facebook friends who delete you as a friend? why is this? what did I do wrong? please help me?

You're seriously putting way too much thought into this... Like you said it yourself, they are from the 'past', it seriously doesn't matter if they don't want to be your friends now... You'll meet new people, who cares about them honestly, you seem like a nice person if you're stressing out about this unimportant issue, heh... Just keep it moving, live it up, don't stress, and relax! :)