If she’s hot, fun, and social then her number is wayyy higher than anything you’d be comfortable with and you’ll probably never know. If you’re judgmental, then you’ll always get her PR version (“I’ve only been with 3 guys and I haven’t had sex in months” lol). If you’re nonjudgmental and tell her you like a women who know what she’s doing and she’s too innocent/inexperienced for you, then you might get something closer to the truth (but even then there are guys who don’t count—even to her).
Look, I get the whole hang up on STDs and good girls and all that—I used to be the same way—but if you want a fulfilling sex life, it’s something you’ll have to get over. Just use a condom and you’ll be good. Fear of STDs is overblown anyway. It’s something that’s drilled into your head in middle school health class to keep you being a good little boy who’ll be a good little provider someday. Here’s the truth: Pretty much everyone who has sex’ll get HPV. Something like 80% of the population has it (girls born after ‘95 in the US were vaccinated against all the bad strains, so you’ll probably be safer with them). Most strains are asymptomatic and doctors won’t even test you for it. Chlamydia, gonorrhea, and syphilis are all easily curable, though there are antibiotic resistant strains so wear a condom and get tested. Your chances of getting AIDs from P in V are almost nonexistent.
That pretty much leaves gentian herpes as the biggest threat. And ya that would suck. But, again, wear a condom and pay attention. Look out for any sores—most girls who shave will have razor bumps at some point, so look up some pictures to know the difference.
If you’re really paranoid, take a hot shower afterwards and use antibacterial soap. But it’s all just not a very big deal and you’ll be fine. You’re much more likely to permanently damage your health driving in a car than sleeping with some girl, and the latter’ll be a lot more fun. Oh, and wear condoms—the biggest potential risk of sleeping around is knocking up the wrong girl (way more scary than any STD IMO).