If you don’t use protection when engaging in sexual activity, such as eating a girl out, that’s a personal choice you make. You know you’re still a virgin, but you’re taking her on her word that she’s a virgin as well. You can never be 100% certain what she’s done with others. People lie. It’s just the truth.
Dental dams are the way to protect yourself when you go down on a woman. It’s a thin, rectangular piece of rubber (like a condom) that you put over the vagina to prevent any fluid exchange. (You also would use this for any mouth to anus play – rimming/analingus.) Almost everything is the same when you’re eating her out, the only difference is that, like a condom, there will be a thin piece of latex between you and her vagina. (If you’re allergic to latex, they make them in silicone too.) This video shows you what a dental dam looks like and how to place it over the vagina.
If you choose to engage in any form of unprotected sex, even when eating out a girl without dental dams or going down on a guy without a condom, you have to acknowledge and accept the fact that you are taking a risk. Both of those acts are often glossed over when it comes to safe sex because a lot of people either don’t realize the risk they’re taking or they choose to roll the dice and hope for the best. A lot of people take the risk and do just fine. Some aren’t as lucky. Use your judgment and choose your partners wisely.
Just know that, YES, you can get STD’s that way and, YES, it could happen to you. Just because you can’t get pregnant through oral does not mean that oral sex is “safe sex”. You could easily get gonorrhea in your throat from an unprotected blowjob or herpes/genital warts from unprotected cunnilingus. It can happen! That’s all I want people to understand. That it’s possible. You are not immune.
Now, it’s highly unlikely in your case, for your particular situation, but it’s good to know for the future! Up to you!
Additionally, you always want to have routine STD screenings when you’re sexually active. Trust is an essential part of a relationship, BUT you still need to protect yourself. So even if you believe with all your heart that your partner is committed to you and can’t possibly give you an STD they contracted from someone else, you still need to acknowledge that it’s POSSIBLE. So always be safe, protect yourself first and foremost, and get yourself tested on a regular basis.