First of all, it sounds as if you have a very distorted self-image.  It would be easy to say you are overly focused on the physical aspects of what makes a person 'relationship-worthy' and that you need to redefine what truly IS the criteria for a loving relationship (you DO), but to dismiss your feelings about your appearance as something you simply need to change in your mind and heart would be unrealistic.  Because, like it or not, how we SEE ourselves, even when distorted by an abundance of self-criticism will always be partially due to the reality we see in the mirror.

So I guess maybe my first suggestion would be, what can you do to improve how you feel about the way you look?  Because once you begin working on what you CAN change, you will find that your mind and emotions will begin to ease up a bit on how severely critical you are about yourself as a whole.  My first (and easiest) suggestion would be to start eating healthier and exercise.  You are naturally thin, so some weights would be a good place to start as there is nothing more ego-boosting than seeing muscles develop and it can be as quickly as a few weeks of even light weight training that can show you some positive results.  So picking up some free weights and working out with them daily might be a first good step.  Also, some kind of aerobic activity would be good, walking, running, jumping -- maybe purchasing a treadmill, these are all good things for the MIND as well as the body.

Secondly, did you know they have come very very far in reversing the damage caused by acne scarring?  I know there are light/laser treatments that have amazing results on the scarring left from acne (dramatic results after just a few treatments).  I am not sure about your financial position or how expensive these are, I think maybe not totally out of reach for the average joe, but maybe saving up for a few of these treatments for your face would also be a very good thing to help change how you feel about your appearance.  Also, go on some of the other forums and ask about natural things that can help reverse scarring, these curezone forums are an excellent source of good information about this. 

You will be amazed how simply taking action to improve the things you can will bolster you up to begin thinking 'bigger' about who you are -- your mood will definitely improve with exercise and a clean up of your diet.  You would be astounded to discover how much a toxic body can poison your mind.  I also would recommend oil pulling/swishing (see the forum) another simply, easy daily detox you can do that will GREATLY improve your emotions and sense of well-being.

I think the last thing I would tell you is this: not having experience with relationships in no way precludes you from having a loving, healthy one.  EVERYONE starts out clueless, and many people are broken, cruel people from terrible family backgrounds with a thought for no one but themselves (or unable to have normal, loving relationships due to the emotional scarring of their childhoods).  You already are way up on the chart on a LOT of people out there,  you seem articulate, aware, caring, sounds like you had a loving family and decent childhood, and other than an extremely distorted idea that all that matters to a potential romantic partner is that you have a perfect face or body -- seem fairly balanced in your thinking.  You are comfortable with spending time with yourself, and I think that is going to play a big role in how overboard you end up going in your first romantic relationship (and yes, you will have one).  I think rather than worrying about 'being such a loner' you will find yourself having to stop yourself from diving head first and wanting to spend every waking moment with the person that falls in love with you.  So being comfortable alone will definitely aid you in the tempting desire to smother your other.

So?  You can start right now with making some positive changes that can only help how you feel about who you are....I suggest exercising DAILY (easier to stick with) and changing your diet.  You can also start oil pulling right away - go read up on it - I tell you you will be amazed at how quickly your mood will lighten once you begin doing these things.  You will begin to feel a sense of positive change happening for yourself physically and that will help your mind and emotions to start dumping all of that garbage you have been feeding yourself over the years about how unlovable you are.  

One other thing is you need to quit feeding yourself these poisonous thoughts about how unlovable you are.  All these negative thoughts WILL play a part in how others see you, so changing the rhetoric in your mind will also be a very important change you need to incorporate.  As cheesy as it sounds, positive affirmation replacing your normal thoughts (and trust me, cutting these bad thoughts dead in the water by overtly and conciously replacing them with good mind phrases IS an exercise all in itself) needs to become habit with you. 

Aren't you fed up bullying yourself?

I think that you are.  Maybe it is time to learn how to love yourself a bit.  Treating yourself WELL by doing good things for  yourself is the first step.

Good luck!