It is not harmful to you but before you check is your boy friend is having any disease like Aids and Hiv
So your GF is cheater or she use like napkin. Are you sure she is 2/3 not 10/14. I am not sure but it might be possible ,only you are in her life. About Kissing ! No comments.
Now that's a load of BS. You have to swap aprox. 2 liters of saliva to pass the virus. Plus HIV is not the same as AIDS. People use it as if they were the same disease. They'r not.