I agree with RockRose. Anxiety finds a place to land. It's manifesting as fear of STDs today, but if you were to convince yourself that you don't have an STD or any chance of getting one, it would probably manifest as fear of pregnancy tomorrow, or something else. She's not kidding about saying "But what if the tests are WRONG?!?!?!" I see that one all the time on the DNA/Paternity forum. Anyway, see a good therapist about anxiety, and work on that. It will help you in every way.
not to add to Your anxiety BUT I fail to understand why so many seem to think that oral sex is not sex
You/He are putting/taking anothers' genitals into an orifice/mouth.
Don't think You are 'protected' from disease with oral sex as std's CAN be contracted orally as well.
It's really up to you to decide when it's appropriate to consider yourselves in a relationship.
But about the STD anxiety. No amount of proof that neither of you has an STD will be helpful for you. This isn't about an STD, but rather about a pattern of anxiety in your mind that has rested itself comfortably in the fear of contracting an STD. If you get the results and they are negative, you will feel a flood of relief that will last about 5 minutes, and then your anxiety will begin to rebuild the wall brick by brick. What if the tests were wrong. What if he didn't have an STD when he got tested but now he does. And on and on.
Rather than trying to prove to yourselves that you don't have an STD, the best way to go about this is to talk to a doctor about your anxiety and get that relieved.
Best wishes.