This is a tough issue and may require some professional counseling from a dietitian or eating disorders specialist. There is really no reason to feel guilt for nourishing your body the way it evolved to be fed. However, societal pressures can lead to feelings of guilt. Outside of consulting with a professional, you might try offering thanks to the animals for nourishing you before you eat a meal. It can also be helpful to connect with other people who did not thrive on a vegan or vegetarian diet and who have gone through what you are going through.