At my last checkup the doc said I might have an STD that can affect fertility. I've only ever slept with my boyfriend, so there's no question where it came from (for me, anyway). I know he's had many other girls but he told me he'd been tested. I was tested when we first started seeing each other and was clean. I'm very upset because this could hurt my chances of having kids. How should I ask him to be tested again, and how can I find out if he cheated on me?