its alright to be nervous or anxious about such potentially life altering disease.
been there done that. now that you have your negative for an ultralow risk. you should move on. im not mentioning a 3 month confirmation due to already low risk, plus the girl is a friend of yours "hiv free". your safe, stay safe remember protection is key.
relax man, you dont have it.
You said: "I started then to think of my last exposure to HIV..."
Let me point something out here: you did not have an exposure to HIV. You had protected sex. Performing or receiving oral sex on a female is not a risk factor for HIV, nor is protected sex. So, even if the woman in question had HIV, you didn't get it from her. Your latest test is sufficient to show that you are HIV negative, and, in fact, you didn't need to test at all.
In short, you did not contract HIV from the encounter that you described, and you need no further tests.