OP - your post is very vulnerable and heartfelt.

You are TRYING to be stronger, but admit you are still weak.

I agree with you.

And it's not attractive.

She keeps coming back because she wants to see if you really are stronger...and when you keep showing her that you're not, she's like "well, this isn't new..." and so she loses interest again.

I wouldn't BLOCK her...but I wouldn't respond to her immediately...and I would move her WAY down on the priority list. Understand that when she's reaching out, it's selfish on her part, and cruel too. She's purposely getting her ego inflated at your expense.

The more you ignore her...focus on yourself...tell her you're busy and have plans, etc...the more she'll be interested. It sucks that it's sorta game playing, but not if you mean it. I think you should have the mindset that this relationship is OVER, and to focus on yourself. And IF she wants you back - make her EARN it. She's the one who left...to date around no less...why are you so desperate to let her back into your heart when she clearly has no respect for you?

Be strong buddy.