Hello, I know exactly how you are feeling, I also have a 3 year old in preschool and she has been sick a couple of times. If it makes you feel any better, in the 4 times she has V* I have never caught it. Keep washing your hands!! don't touch your face, and don't kiss him/her (I know that sounds weird, but my husband always kisses my daughter when she is sick and he usually catches it.) My daughter has been in school for about a year and a half and she has only had a stomach virus 2 times since she has been there. It was tough for me when it happened but we got through it as a family. My husband knows how I am and he is also very supportive. You will be okay I promise. Just take walks, deep breaths, long showers, and do your best to remind yourself that you will get through it.
Best of luck to you
Keep Smiling.