You've come this far, don't falter now!
Concentrate on you, why aren't you meeting new people? Get a circle of friends going, join a club, anything to occupy and enrich your own social development.
If her being on facebook hurts or causes you to think about her more then remove her! You can always try being friends with her much later on when it isn't an issue (but by then you'll be thinking, why bother?!)
If she messages asking why you removed her just say seeing her pics/updates etc brings back to many memories and you're finding it hard. No need to say any more than that.
"Never make someone your priority, when to them you are only an option"