My boyfriend had unprotected sex with his ex.Could he be a victim of STD?

My boyfriend had unprotected sex with his ex girlfriend.Not many times,they had just once or twice.She took pills immediately.Its been more than a year since they parted and now he is with me.I am a virgin and his ex was also a virgin before she had sex with him.What is the chance that he has STD? Its sort of embarrassing to open this topic to him.I fear he may get hurt but at the same time its kind of disturbing to be knowing,that he had unprotected sex with someone.Just wanna know if i can ignore this or is this to be worried about? If a guy has sex with a girl who is a virgin, are there chances that he may get STD? And if the same guy has sex with another virgin after a year or two, will he get/transmit STD? There must be a lot of divorcee's, widow/widowers who remarry.They may be having children with both ex and current spouse.Whats the case with them?