There’s really no way to tell if a person has had intercourse yet, so if you’re in a relationship with someone, it’s a good idea to ask them. Besides not being able to tell if someone is a virgin, there’s also no way to tell by looking at someone if they have a sexually transmitted infection (STI). The person may not even know if they have an STI.
Having sex is a big deal. It’s a good thing to ask the person that you’re thinking about having sex with if they’ve ever had sex before, if they’ve used protection (such as condoms) in the past, if they’ve been treated for an STI, and if they’ve ever been tested for STIs and HIV. If you’ve been sexually active it’s worth it to get tested for STIs and HIV before having sex again. Finally, if you’re thinking about having sex, you should talk openly with your partner about how you will prevent STIs and pregnancy.