My friends online and in real life, sometimes ask me about stuff and one topic was how some break-ups could occur "out of the blue." But I told him that no, it doesn't just happen like that.
It's not what a guy thinks concerning what will make his girl happy, it's what she tells him about what will make her happy that counts! If he ignores this, then she'll be gone...because he just didn't listen.
By telling, I mean: her reaction, body language, mood, communication, etc. Remember that just because you stop fighting about things doesn't mean that it's not an issue anymore. It's that she's given up for whatever reason.
Then when it's too late, it doesn't help to blame it on everything or anyone else and think that you had no part in it, because then even your friends (the honest ones will just tell you you screwed up, and learn for the next relationship) will know you left things out of your story.