idk how to start this conversation

i went to my ob last thursday got a pap smear and a u/s . just like an hour ago i got a call and they told me i have chlamydia . ive been having sex with my boyfriend of three years . ive never cheated . but i need to tell my boyfriend tonight about the call but i dont know how to go about the way to start the conversation . i know when i try to tell him im going to start crying because i never thought this would happen to me . ive known him since we were 10 and hes never been that kind of person . ive told him before if he ever cheated or anything just be honest and we could work something out . but im just so confused and idk what i should do .