Alright, so after reading through all of this I can't really answer the your direct question "why women cheat," however I do have a few things to say that may help you out, or just give you a new perspective on the issue.
1. For someone who is critical of another using "sweeping generalizations," why are you trying to answer why "women" cheat? Each of your relationships, and each of those girls is their own person with probably thier own reasons, and as someone else has already pointed out, by focusing on the fact that they are "women" and so totally different and complicated then "men," you are in fact doing the exact opposite of what you say you want to understand; instead of really trying to understand these women and thier actions, you are only dehumanizing and alienating them. They are people too, and are capable of humankinds worst parts and most wonderful parts. I doubt they all behaved they did for the same reason, why did you never ask them when it happened?
2. This brings me to the next part...and this could very easily be misconstrued as offensive. I do not know you, or the intricacies of each of these relationships, but it seems to me in descriptions and in your responces to others' thoughts that you are VERY defensive. In anticipation of other's judgements you think of every possible way in which you were the RIGHT and well-behaved member of the relationship, and she was the irrational and undeserving one. You may very well be right, I am not one to judge. My point is, if you truly are trying to figure this out, maybe we need to calm down a bit and turn the critical lense on ourselves? If you suspect that these events are more than just a string of bad luck then you need to really observe the common denominator here; you. Keep an open mind. I highly suspect there may have been things and signs coming from her end of the relationship that maybe you just didnt realize at the time? I doubt all of these girls entered the relationship with the sole purpose of decieving and betraying you, so think back, and this time be ready to accept SOME responcibility for the way things happened. Also keep in mind that that doesn't mean that you are flawed, it is just an opportunity to learn something about yourself, something that might improve your future relationships if you are aware of it.
3. Also, in defense of another poster, there IS something unnattractive about a person, male OR female that pours ALL of themselves into the other person. Infact, it's more than unattractive, it's unhealthy. I know, the cliche is that a woman wants a man that is all about her, ready to die, ready to fight for her, etc. Let's get real, we don't live in caves anymore. Love is not about starring endlessly into each others eyes, love is about standing together and observing the world. A healthy relationship invloves two people who can stand on thier own two feet and respect each other for the individuals that they are. Of course, there is alway vulnerability and needs when it comes to couples, but it shouldnt be a constant all-consuming drama. That kind of thing reeks of emotional instability and avoidance of one's own challenges.
4. Both you and the females involved (I am assuming) are still really young. Meaning there are probably things like school, jobs, and general basic life choices that are hashing themselves out for both of you. At this age, you are SUPPOSED to be experimental, try new things, expose yourself to new ppl, etc. This is in NO WAY justifying cheating, it is well within thier power to end the relationship before moving onto someone else, however it seems in all cases you were way more invested in the fairy tale then she was. In my experience, as stated in the point above, it is very easy to distract oneself from the harder more scary choices (school, money, etc) by making a person and a relationship your whole world. Maybe a little bit of this is going on? If it is, can you understand why this may be a little suffocating for the other person? Like I said, I don't know you, these are just thoughts.
I'm sorry that you have experienced so much abuse in your relationships, no one is deserving of that even if they are not the perfect mate. I hope that you do find someone who makes you happy and treats you with respect. Also, I hope that you can find room to forgive these girls of thier wrongs and that you do not let your lack of trust pollute possibly wonderful relationships in the future.
p.s. pardon the poor spelling and grammar, it is 3 am
