how do I know if I orgasm from oral?


so my boyfriend is really really great at eating me out, but every time I've ever been eaten out in my life, I can never tell if I came or not. is there a way I'll be able to know? my boyfriend has never told me if he thinks I came or not, but I've also never asked, in fear of hurting his self esteem. I always come during sex tho. what could be the issue?