Most of the time when your girlfriend dumps you...it's not her, it's you. Guys, we're some of the dumbest oafs around when it comes to relationships, and we're always doing SOMETHING wrong. Girls may not be the easiest creatures to understand, and relationships with them can be a bit difficult to manage...but really if you can figure out your problems you can solve them.
That's why I'm writing this for you, as a friendly man-to-man resource for a few of the things we frequently do that tick our ladies off and make them want to leave. Sure there are women nice enough to painstakingly list off our every faults for us, but not every guy is so lucky as to have one. Not to worry, bro...I will help you through this madness.
1) First main thing that girls really despise when men do is when they don't pay attention to them. This really drives a girl nutso, because it can feel like they require our every waking moment to be devoted to them and only them, or else we don't love them. Of course this assumption is completely false, but girls seem to need us to pay constant attention to them.
NOT paying constant attention to them makes them think we don't love them, but when we DO pay constant attention to them they start acting like we're freaks. There IS a happy medium somewhere in there, but the exact level varies for each girl. Best solution here is to simply listen to her and figure out what she specifically needs, attention-wise.
2) There's this concept that women have, called "emotional support." They need their guys to be "emotionally supportive" of them. Best as I can figure it, it's kinda related to item number 1 on this list, but a little more expansive. Girls need to feel like their guys really understand them, and can get to know them almost as well as they know themselves.
Guys who can do this naturally are referred to as having "game." This simply means that a guy is naturally good at reading women and understanding the things to say and do to make their hearts melt. Your supreme goal here is to make the girl feel like she and her feelings are both very important to you...and the best way to do this is to really listen to her and read her body language.
3) Women really kinda hate it when guys cheat on them, even if some of these same girls would gladly cheat on their guys. Of course we all realize this is a no-no, and wouldn't be too happy if our girls cheated on us...but sometimes we either have a momentary lapse of stupidity, or we don't realize what exactly constitutes "cheating" in the female mind.
You don't have to have sex with another woman to be "cheating." A lot of the time all it takes is a single look of appreciation at another woman's finer physical "assets" for your girlfriend to take offense. Even fantasies about pornstars or celebrities can be a no-no, it just depends on the girlfriend. Best and safest bet is to forget that other girls exist, and think like they're just other guys who look different.
4) When you're living with a woman, helping around the house can become a sore point...she expects you to do it, and you don't want to. I understand not wanting to get up and clean stuff or take out the trash, but you have to really consider whether or not it's worth ticking your girlfriend off. Take my advice...just get up off your lazy butt and do a few chores.
So how does this help you if you've already broken up with her? Well, once you can identify the things you've done wrong in the past, you can start working to avoid doing them in the future. Whether it's with your now-ex-girlfriend or with a new woman, you'll be much less likely to make her leave again if you can keep from making these idiot classic "guy" blunders.