My boyfriend is getting boners around other girls...

Paige
Within the last week my boyfriend went to his best friends house where his best friend Ryan and Ryan's wife Kathy live. Ryan's sister was at the house as well and they were all playing video games and my boyfriend said that when he was playing a game with Ryan's sister that he got a Boner and he said as if it was a joke and I thought I would just try to laugh it off but now it's really bugging me knowing that he's getting boners around other girls because this is not the first time this has happened. We are sexually active, but not often due to work schedules and alone time. What should I do..?