Absolutely FREAKING out!

I know what I did was dumb, so I don't need to hear about it or that I shouldn't be having sex. Thanks. Anyway. I've been seeing this guy for like a month and he has been with 27 women. I've only been with one guy. I asked him about STDs and he said he was tested two years ago and was fine, but he's been with 3 or 4 girls since. He said he would go get tested again before we had sex. He hasn't been tested yet, and me, being an absolute hornball and not thinking, gave him head the other night and swallowed. I absolutely trust this guy and know that if he had something he knew of he would tell me. But I'm afraid he has something he is unaware of. I'm completely freaking out. I know all I can do is get tested. But what are the chances of me getting something from him this way? Or the chances of him having something, considering he had been tested after the majority of women he had been with and didn't have anything.