Need a woman's perspective!!

Thank you in advance. Would really appreciate some candid assessments of my girlfriend.

Great relationship for almost 2 yrs....always trusted her to be honest with me....

Girlfriend has became emotionally involved with her good gf's ex-husband. She was a bridesmaid in their wedding. The two of them have been friends for over 20 yrs. The 4 of us used to go out to dinner, along with their recently adopted boy. After our last evening, March 09', just a few wks later, the wife split. Completely blindsided, the husband reached out to my gf, in hopes she could track down the wife for some explanation. I always trusted her and felt if she could help him, fine. I sensed during that last evening out with the four of us,there was clearly tension in the air between that couple.

End of August, gf and I had a positive discussion about our future and how she wanted us to take a break for a while. She didn't want to break up, or date other people, but rather, focus on her career, and try to get her head straight about her future. At the close, we had a great passion filled nite of sex. Less than 3 weeks later, I saw her car parked in front of her friends former house, and in front of her ex's car, early one morning. Presumably, he leaves for his grunt job before her. The two are now divorced, as of this past July. He lives, literally just a couple of miles away from my home. Since then, her car is there 2-3 days a week. Her past is filled with incredibly bad decisions. Divorced twice, and the boyfriend prior to me (her 1st love- then reunited with him 5 yrs ago) were all horrible. They all for some reason sought sanctuary from her, each evacuating to either the basement with drugs and alcohol or on the town with other women. I come along, I'm gainfully employed, well educated (none of the previous guys were including the friends ex. they're all low wage earners) The first 2 husbands were actually subordinates that reported to my gf. They way she discussed them, according to her, they were all losers who mis-treated her. Of course, I've never heard their side of the story, as I never really cared. I'm very confused by all of this. 2 wks before our "taking a break" chat, she actually asked my mother whether she had announced at her recent family reunion (which we couldn't attend) the newest member of the family, her? I overheard this! Comments like this reinforced my feelings for her. Just prior to that, we had discussed who her bridesmaids were going to be and how she wanted to move in before the upcoming holidays? This was all just weeks before our "take a break" chat. I might also add regarding the boyfried prior to me (throughout our relationship) she has maintained a close relationship with his sister-n-law....this guy is literally circling the drain, having recently this past summer not only lost his job, had become addicted to crack cocaine. Of course the sister-n-law dragged my girlfriend back into his life asking her for help in organizing an intervention this past July. She literally spent hours and hours cleaining his house. I've tried taking the no-contact approach, though she has texted me messages out of the blue. Last week I sent her a very harsh email pleading with her to start making good decisions in her life. Alluding to her poor decisions of her past.I also mentioned that I was pretty confident that her "former good friend" didn't appreciate the fact that she was sleeping with her ex husband. Clearly I've pissed her off...she has yet to admit or deny her involvement. Either she thinks I'm stupid and don't remember where they live or she's embarrassed or ashamed of her decision.....either way, I'm very confused as I was clearly the best thing that ever happened to her...perhaps I wasn't "needy" enough for her, or possibly she knows I'm too good for her, and she needs to lower her bar. Either way it's a tough pill to swallow!