Asexuality

I'm 16 and asexual. I told this to my boyfriend before we started dating. After explaining what it was, he took a few moments before saying that he thinks that he is too. I took this information with hesitation because of some stuff he had done with his exes. I don't know if he said this to make me trust him, or if he said it because he actually thinks he's ace. Is it bad that I don't believe him because he's had sex before?