How to survive in this world completely alone?

(This post is going to be somewhat lengthy, but this is a serious question and I am in desperate need to know the answer to. Thank you so much for baring through it and giving me your opinions and feedback, it is greatly appreciated. It means so much to me.)

This is a question I've always needed to know because, generally throughout my life, I have never been alone. Let me explain:

I am a 20-year-old male college student and having been living with my partner for around eight-and-a-half months (since mid-October of 2014, and it is currently June of 2015); I met him my first day of college (which was August) when I had just turned 19, and by the time October came around we had become an official couple and by Halloween I was living with him and his five roommates. I know that sounds crazy and all, but my partner and I have a great relationship and we are both mutually happy with one another. He is nine years older than I am.

Before beginning college, however, I lived and shared everything with my identical twin brother (who ironically has the same name as my partner). For the first 19 years of my life I was always sharing everything with my twin brother as well as my three other brothers, whom I shared rooms during my coming-of-age. It was not until college that I came out of the closet, met my partner, and moved away "on my own" for the very first time with people who aren't my family members; although I am not necessarily "on my own" because I live with and share everything with my partner now instead of my brothers.

Essentially, throughout my entire life up until this point, I have never been alone and completely independent. I am blessed with that I have never been alone up until this point, but I feel as if that never experiencing being alone has made me automatically become codependent on others on everything: my financial stresses, my happiness, my feelings and opinions of myself based off of what they say they think of me, etc. I have recently discovered that I am emotionally dependent on my partner and that throughout my childhood and teenage years I have always been a pushover and a people-pleaser. I always feel the urge to make other people happy except myself and am extremely codependent on others, and that reflects on my well-being.

I am worried because here I am, a 20-year-old who does not know any type of independence. Emotional, financial, etc. I am in college to build myself, find what I like, and to learn how to be an adult. However, I do not feel this way at all because in order to become an adult, you have to learn independence; and I need to learn how to survive on my own but I don't know how to.

I am in a happy and strong relationship, and by no means am I doubting my partner's faithfulness and love to me. However, anything can happen because people always change and, excuse my French, **** happens. I realize that no relationship is ever perfect because perfection is unattainable. Even married couples can find that things aren't working out, that is why the option of divorce exists. Acknowledging this, I can say that this relationship could or could not work out just depending on if it was meant to be or not (which, in turn, takes time to find out because nothing happens overnight). I would love for it to work out because I adore my partner and have confided so much in him as well as inputting all I can into this relationship, but the point that I am making is that I cannot fully place faith of my future within this relationship because than what will happen if we were to break-up? I would have to move back in with my twin brother and cope with the fact that I had just lost a relationship I had invested all of my heart and soul into.

The question is: How do I learn how to survive in this world completely alone? My whole life up until this point has been surround by people who have supported me and I feel as if that has hindered my concept of what true independence is. Hypothetically, if this relationship were not to work out in my favor (God forbid) and I have to go back living with my twin, how would I be able to become my own person? How do I learn independence and stop feeling this innate codependency on others? I crave independence so badly; I do not have a job because I do not have a vehicle and would have to carpool with my boyfriend but wouldn't that be defeating the purpose? If it ever happened, I want to be able to know that I can support and take care of myself 100% and be happy living by myself without the urge of any kind of dependency on others?

Thank you for taking the time to read all of this, I apologize and I know it is lengthy but this is so serious to me. I really need outside feedback on this. I need to become an independent adult. I need to learn how this world really works and how to survive being on my own, by myself. Again, thank you.