How can I manage my emotions? How does one not be so reactive and defensive?

Hi T, thank you for your question, it can take courage to express how you are feeling so openly as you have done.  

Emotions, thinking and acting/reacting are all linked.  It sounds like you often act in a way that later on you think perhaps you could have done it differently.  Communicating how we are feeling is difficult if we do not do it enough.  Having the right vocabulary for the moment is hard.  Knowing what to say and how to say it can seem impossible at times.  I think there are a few things to bear in mind.  

1. Our brains are wired in such a way to keep us safe.  You react quickly because of a perceived threat and you need to defend yourself from it.  Perhaps you have been hurt in the past and do not want to be hurt again.  This part of our brain works way quicker than we give it credit for.  To slow this down takes effort, but can be done.  Try and slow down in others areas of your life.  Make a conscious effort to stop before you react.  This will give a chance for the rest of your brain to catch up and so you can respond appropriately.  This takes practice, so practice it in other areas of your life, in situations you are in control of, taking a cool, calm and measured approach.  Building this routine can help when you are in more difficult situations.

2.  Talking about emotions and how we are feeling can be hard.  Practice by speaking up when you need or want something, gaining confidence in explaining to someone else what you need will build confidence as will expressing to others how you feel.  Perhaps after a film you could say 'That film made me feel really happy/really sad!'  Practice doing this at least once a day.

3.  As you become more confident in communicating your feelings and it becomes more natural to you, you will build the vocabulary and self-awareness and will have a great insight into your own behaviors and they will change for the better.

Because our thoughts, emotions and behaviors are all linked, if we can change one thing in the cycle it will change the outcome overall.