<human>: Okay a little background, this is my second LTR (first one was 4 years). I dated this girl over the past two years and it was on/off after the first 6 months, which was a bad sign from the start. A problem I have is I often like to see the good in people so I give them too many chances.

So far there has been 3 separate occasions where we ended because she wanted to date another guy. The third time just happened this past Thursday out of nowhere, but this was just like all the past times. Every time she will date the guy about 3-4 weeks then come back at me with a wall of text saying how she made a mistake and wants to come back. She has pulled this same stunt about 5 times after we've been broken up for a period. Other times I have resisted slightly, but have been tricked by false futures, sexual motivation, and generally feeling bad. This is obviously a toxic relationship and I know I need to stay out for good and move on. She has underlying self-esteem issues that I will never be able to fix. 

I am mainly looking for people who have been in this situation before and successfully ended it with someone. I know that 3-6 weeks down the line, she's going to try and contact me. So far I've blocked her on everything imaginable (aka NC), but in the past that didn't work because she would leave letters (10-20 pages) in my mailbox, come to my house at random times, and etc. 

Sadly I'll never understand why she always comes back and it would be a blessing if she actually found someone who she could stay with. I need to put this girl in my past and get on with my life hopefully finding someone who doesn't cheat.

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Dated girl with underlying self-esteem issues, worried about the impending "I need you back" stage that always comes about. Need advice from people in similar situation and how they successfully cut someone out of their life.