Hi burnerin
You're definitely not alone with cheating being a major cause of the end of these relationships.
Here's the poll result from Skip:
What was the final straw that ended the relationship?
More than half of all responding members described cheating as a major factor to the termination of the relationship.
I was thinking about everything in our relationship that happened the other night and I came to this conclusion because she would always be upset with me thinking that I cheated.
This came up in my relationship maybe dozens or even hundreds of times. She used it consistently when projecting problems.
The first time she broke up with me she stated she was thinking about men... .I know a couple of men who were interesrted in her at the time.
Ditto, many of us here.
She claimed that when she was feeling sad she wanted to be with a girl, and when she was happy she wanted to be with a guy.
Similar to my relationship. In my relationship, she actively went to look for relationships with women.
One time her ex texted her saying he missed her. She told me about it, but then said "I have to go get closure with him. So she flew back to her home state to get closure." I think she cheated on me then. She swore up and down she never cheated on me.
Ditto, your situation.
This will help: I found out months later that she did indeed cheat on me during that instance.
Then one time, she went to Chicago she told me that there was this guy at the bar that was interested in her and she didn't do anything with him. Should I be believing that?
Ditto. I spoke to my ex while she was at the man's house.
There was also this guy prior to our relationship that had had sex with her and kept begging her for sex. I'm not sure why she didn't block his phone number.
Ditto. It drove me up the wall that she would continually put herself in the same position with the same men. Did it have the same effect on you?
When we finally broke up she told me she didn't know if she could even be in a relationship. That she had to figure that out. She told me she was toxic, and I just couldn't understand why she was toxic.
Ditto.
It's giving me closure to realize this. The fact that she was trying to protect me from herself makes me forgive her. She was right. I was too blind in loving her to see the facts. She kept saying she didn't deserve my love and I didn't understand why, but now I do. The fact that my mind has finally come to a conclusion to lay the rest of why the relationship went so bad. It really isn't my fault at all. It is all hers. I just wish I would have broke up with her the first time she wanted to before it got to bad.
... .
I still care for her because she was only trying to protect me, but I am so glad for my awareness of this mess.
Yes, you're right, that may be one reason. If you can find forgiveness through this perspective, I think that's a good thing. From here, I encourage you to recall that BPD is a complex disorder. Therefore, assuming one stable motive (to protect another person) for the behaviour of repeating unstable relationships could be incomplete. Try to recall the shades of grey--"too blind in loving" and "all her" fault don't seem very grey.
Moreover, assuming a such a "noble" motive may lead you to feelings of obligation and guilt.
To me, I feel that you may be looking for excuses for her or you. It may help you to heal if you try to convince yourself that she's better than she actually is. But, I offer that it may be much easier and healthier in the long term to confront the want and live with the reality of having an unfulfilled want of a relationship with a disordered person. See this
link.
From here it might help to step back and see other reasons why she has impulses to gain pleasure from physical relationships. Investigate your closure and try to take it further.

Sometimes, it may seem there's a lot of facts--use self-compassion!
I hope you find peace.