The flu virus infects the respiratory track and is transmitted between different people through respiratory particles. Basically the way it works is someone with the flu coughs and small invisible particles of respiratory secretions and saliva that contain the virus are spread. Often times these particles hang out in the air for some time before a susceptible person breaths them in. The best way to prevent the spread of flu from one person to anther is by avoiding that person all together. If that is not possible, then the person infected should where a mask to help prevent the release of those respiratory particles. Of course you should also not exchange saliva with him because this type of contact can also spread the flu. Although semen, blood, and tears do not tend to carry the flu virus, if you are close enough to him to be in contact with those fluids, then you are close enough to breath in the infected respiratory particles
Remember that a great way to reduce your risk of getting the flu is for you to get the flu shot
. If you have not received it this year, then I suggest that you schedule an appointment with your primary care physician
so that you can get it. Good luck.