Men are complicated beings. That's especially true if you're deeply involved and in love with one. Love isn't always the easiest path to travel. There can be bumps along the road that lead to confusion and uncertainty. Sometimes a man can react to things in a way that simply doesn't make sense to us. Such is the case when a man suddenly disappears. This happens much more frequently than most women realize and once it does happen to you it's devastating. If you're asking the question, "why did he run away from me," you need answers. Trying to decipher his actions may feel impossible but there are reasons why men do this. Once a woman understands the motivations behind why her guy suddenly bolted from the relationship she can then start to feel in control of her emotions and life again.
Whenever a woman asks the question, "why did he run away from me," she's looking more for a fault in him than in herself. That's completely natural given the fact that you had invested yourself heavily in the relationship and he was the one who decided to dump you. Sadly, the main reason why men leave a dating relationship is there is something about their girlfriend that suddenly turns them off. It can be something as seemingly innocent as calling him too often to something more serious like pushing him repeatedly for a commitment he's not ready to give.
Many men can't deal effectively with communication in their relationship. If they don't feel fully invested they don't see a problem in heading for the hills as opposed to staying and working through any issues. Most men shy away from confrontation and will actually do anything possible to avoid it. That's why if your guy was turned off by something you did he may see leaving as an easier way to handle what he feels.
Sadly, some men don't even have the courage to say goodbye and instead they slowly disappear over time. You may sense that this is happening in your own relationship if your man is less available or he has become busier recently. Women have wonderful natural insight in this department and can usually tell when their man is creating emotional distance. If you ignore it, he will eventually just stop calling. It's obviously not the best way for a relationship to end, but it's unfortunately an all too common way for two people to drift apart and eventually go their separate ways.