How to ask BF for an STD test

Kenya

My boyfriend is going to another state to see an artist in concert with his cousin, her friends, and a girl he says is his “best friend” ive never met her cause she lives two states away but i just never liked the idea of a guy having a girl best friend … he is my cousins friend and I’ve never heard him call my cousin his best friend even though they have known each other about the same time (met at the age of 7). After this concert they will be going to a 3 day festival and all of them will sleep in a tent together. I want to trust my boyfriend but my mind wont let me get past my previous trauma. I previously asked my cousin if he was a cheater and he said “you have nothing to worry about with him trust me”. I trust my cousin but I feel like plenty of people withhold truths from their friends … what if he withheld from my cousin that he has cheated in his past relationships. The whole point is how do I ask him to take an STD test without outright accusing him of cheating and without making it seem like I am cheating (which I’m not). I want to be safe cause I’ve been burnt before and now I have scarring on my tubes and via chlamydia and it is why I struggle with fertility now. I just want to be safe.