am i wrong or just overreacting?

my boyfriend and i have been together for a year(anniversary yesterday) and he is 5 years younger than me. his 21st is next month and he's having a party. 3 of his friends hate me and instead of telling them that they should play nice for the night, he instead told me that it would just be easier if i didnt go. is this messed up or what? i wont say anything because i'm trying to be supportive. do i have the right to be angry???