Very typical of OCD. Even as I sit here writing this, I have my own obsessive worries going on.
This is the key. You know this is an irrational thought and you cannot give in to irrational thoughts. You definitely do not have HIV. Kissing is not even a mode of infection. When this thought comes into your head, replace it with a positive one. Say to yourself is this thought a fact or a fiction? Of course in this csae it is a fiction because nobody gets HIV 21 years later nor do they even get it from kissing. Then say to yourself," I am not going to waste my time thinking about something that is a fiction. I do not live in a fictional world but rather I live in the here and now." After a while you will not be plagued by this thought anymore.
If you are having other OCD thoughts, then you may need to consider seeing a therapist to discuss cognitive behavioral therapy or even taking medication.
Medication helps me. I think the thought and can for the most part let it go. Or if it does hang around a bit, I don't feel out of control.
You can be the role model you want to be. You just have to get the OCD under control and there are many ways to do that. No need to suffer with it.