Here's a fact: Everyone gets angry from time to time. So it's not so important that you get angry; what's important is how you express it. Your tendency is to not express anger, but to sit on it.
Why is it so difficult for you to confront and explain when someone has offended you? Instead, you hold it in, chew on it, swallow it and add it to the growing heap of similar situations. Has this behavior affected your past relationships? That's a resounding yes! You see, other people can feel your anger, even if you're not expressing it. It shows in your eyes, your body language, your behavior. A few angry words, which are over in just a few moments, are far preferable to the cold shoulder, which can last for weeks -- or worse, the passive-aggressive behavior you're known to indulge in. Don't expect others to figure out what's bugging you. Just say it. You'll find that your partner appreciates this direct method, and that the whole thing will blow over quickly instead of dragging on for ages.