Hi Loaaol
Welcome to the forum!
I can't give you a definite diagnosis but from what you've described, it sounds to me as if you do have OCD. You admit it is irrational to feel guilty for eating food that has touched another food. It is a classic symptom of OCD that the rational side of your brain recognises it is perfectly OK for one food to touch another but that the emotional part of your brain feels anxious about it. Naturally this mental contradiction feels bewildering, and I fully understand you feel self-conscious and embarrassed when eating in front of other people.
One way of dealing with this is called ERP (Exposure and Response Prevention). It involves repeatedly confronting your fear rather than avoiding it, and then staying in the frightening situation until your anxiety subsides. You would have to eat some food that has touched another food and then try to live with the resulting horrible feelings without trying to lessen them in any way. It will make you very anxious in the short-term but most people find it will knock the problem on the head in the long-term so that you will be able to eat a plate of mixed-up food without feeling any anxiety.
http://www.ehow.com/how_2228424_treat-obsessive-compulsive-disorder-erp.html
Does this sound too difficult? Then you could build up to it slowly rather than dive in the deep end. Start by eating just one crumb of food that has touched another food. After you have trained your brain to cope with doing that, then gradually increase the size of the crumb into a teaspoonful, then into a desert spoonful, then several mouthfuls, until eventually you've overcome the whole phobia. It is easier to tackle it in little steps like this.
I really wish you success in overcoming this problem, Loaaol. I have OCD and I know what suffering it can cause and how it interferes with your social life.
All the best to you,
Luke