You say you bottle up your feelings and emotions and then, once they reach boiling point, you break off the relationship. You have a pattern of blocked communication and this is how it manifests...
You are in communication and the other person is sharing their perspective. You do not agree with it, nor do you accept what they are saying. You start to feel defensive and negative emotions begin to build. You are now afraid of expressing your point of view because you are afraid that with all this anger inside you will say something hurtful - perhaps you also feel that your point of view does not merit being expressed. The result is that you say nothing. Your truth is never heard. The issue between you is not resolved and your anger increases to boiling point. Then you end the relationship, not because you don't want to commit, but because your anger is so intense that you are afraid of expressing yourself. You probably fear that were you to express yourself now you would lose control and maybe do or say something you regret - so you say nothing and walk away.
The first piece of guidance I want to give is to do with how you perceive incoming communication from others. I want you to give up entirely this tendency to see what another person is saying as a threat. I want you to grasp the truth that another person's perspective can always be helpful and therefore to accept in a positive light what others are saying. Life is holistic and by accepting communication offered by others you expand your ability to see the situation or issue from a higher, broader and more enlightened perspective. As you do this your understanding grows. Your improved understanding will then help you resolve the situation to everyone's satisfaction.
To attain this skill, simply become aware every time you seek to defend yourself against another person's point of view - and replace defensiveness with acceptance. In practical terms this means that when someone is talking, take your attention away from your negative emotional reactions and focus outward on what the other person is saying and on how they are saying it. Concentrate on really getting their message. If you can manage this you will never again have another argument or row. Peace and harmony will have entered into your relationships and you will have taken a giant leap toward wisdom.
The second piece of guidance I wish to give is about the skills needed to express your point of view. Although you have accepted the other's point of view you may still wish (and need) to express your own viewpoint. This is healthy and completely necessary in a balanced relationship where two people learn from each other. I want you to practice speaking your truth quickly - do not wait and let the communication become one sided. When you speak your truth, communicate two things together: how you see the situation and how you feel about it. For example, "I did bring the washing in from the rain, it only got slightly wet and I feel irritated/bemused/let down that I am not trusted to look after our washing." Or - "I spoke to the cable company and tried to pay the bill but their system was not working. I feel sad/angry/dejected that you thought I forgot to do this important task."
By seeing the other person's point of view as helpful you will be reducing your tendency to generate negative emotions and by giving your point of view early along with sharing how you are feeling, you will be dissipating any remaining anger and resentment and preventing it build into a mountain of unresolved feelings that threaten the relationship.
In time, as you practice seeing value in the other person's point of view, your negative reactions will diminish and you will no longer react with negative emotions when people communicate with you. At that point you will no longer need to share your negative feelings because you will only have, and wish to share, positive feelings of love toward the other person.
You say you have no spiritual inclinations. As you learn to master the art of interpersonal communication and begin to see and understand how, when allowed to blossom, communication always works for the common good, I challenge you to ask yourself - what is behind this urge to share and communicate - what spirit underlies this creative, problem solving, group intelligence?
Further Help and Resources
If you feel you need further help with interpersonal communication I suggest you take a look at Peter Shepherd's Communication and Relationships Course - it's freely available on Trans4mind. If you are in a romantic relationship you could do this course with your partner. By doing this course together you will have fun and improve mutual understanding.