Anger Management and Relationship Mngmt.

In general, I'm very calm and composed. So, I ignore a few things that disturb me at initial phase. But later when I couldn’t take control over myself and moreover when there is no one else with whom I can share my feelings and emotions, I overreact on the situation till the extent where things become worst and completely out of my control. It happened twice within an year when I chose to take the step which went against my relationship. I truly to want to stick with my relationship till the end of my life. Want to put all the possible efforts. Just needed one assistance from you to guide me that how can I control my anger even at the worst situations. Want to become more positive and avoid negative thoughts that come in my mind because of the insecurities. Want a simple and sorted relationship for the whole life. What changes can I bring in myself to make things better?