You're scared of losing. You emotionally detach a piece of yourself so that you'll never get hurt. Like your inability to commit to a hobby, you are also unable to commit to a relationship. You hate giving too much of yourself away. You like to be control of things, and falling in love will throw a spanner into routine, safe, and predictable life. You're scared to open up to someone else incase they betray you or think less of you. It makes you feel vulnerable.