If the boy does not have an STD nothing happens.
It just goes through your system and is digested just like medic dan said.
Swallowing your friends sperm or him swallowing your won't harm either of you as long as you both don't have an STD.
Is that what you meant in your question.
Kate, you mean to tell everyone that you have never preform oral sex on a man or a woman, and you have never had their seman in your mouth, and swallowed it. Sorry not buying it. I have never gone down on a guy, but i have on plenty of woman. It really makes my day when i can get my partner off with my tongue, and she shoots in my mouth. I love the taste, not only of her juices, but i will also go back down after intercourse, so that i can eat my own juices. Later she will suck on my penis until i cum in her mouth, and we will kiss deeply, and pass it back and fourth while we are kissing. There are times when she likes to watch me masterbate, and then lick the cum off of my hands. Try some of this you may find out you enjoy it.
Knowing who your having sex with and their history just protects yourself have to make sure your both clean and STD free.
i have been wanting to do that for years each year i keep wanting it more and more. i watch gay porn and it makes me crave cum i started eating mine and love it