Cause, guys are different when they are with their friends. They can sometimes be jerks. But you have to think about all of the good times you have with each other and maybe when he is with his friends you won't feel that way. Or you might not want to share him with them.
Guys (SOMETIMES) want to impress either you or the other guys, so they act differently.
You killing me with the grammatical errors . . .
"Why don't I like my boyfriend when he is around his friends?"
We all tend to where different social personas when we are younger . . . One for our closest friends, and the other for the girl we want to impress . . . It appears your boyfriend is one person with his friends and another with you . . . Depending on his age, this is part of discovering one's self.
Have you tried accepting and loving him both around his friends and around you? Maybe he will let down his guard to show which one is the current version of himself . . .