On monday, my bf went out to dinner. a few hours later, he began to feel ill and vomited. the next day, he woke up feeling fine. would this be food poisoning? im seeing him on friday, and dont want to catch a stomach virus if thats the cause.

4 days = maybe safe: Contagiousness varies among different "stomach viruses" and among different people, so is not easily predictable. However, one can feel safer if the sick person wakes up on Day 5 without any symptoms the preceding 4 days. If unlucky, she can still catch a virus and come down with the illness. Food poisoning is usually less contagious, but depends on the bacteria type.