Letting go is hard. But you can do it.
My advice to you will be. Put everything that reminds you of her
away in a box and keep that box hidden away from sight. Seeing them
will remind you of her and we do not want that.
Look and reflect on your actions. You said you guys broken up
three times, which means you patch back twice. Why is this so?
Maybe it's the lack of self discipline from both sides? Learn from
your mistakes.
You know that you should not wallow in self pity. That's great
to hear. This means there's hope for you. Talk to your close
friends who will understand your situation better than strangers on
forums. But of course we can help you with the general stuff
too.