Julie, I just read another one of your posts and saw that you are 14 years old.
Knowing that doesn't change anything that I said in my earlier, except to suggest that you also talk to a trusted adult in your life about your feelings (parent, counselor, teacher, friend, doc, etc.) You're entering uncharted territory and it would help to have an adult close to you that you can confide in, who can give you good advice and warn you about potential hazards.
Other than that, I'll stick to my earlier answer.
You can't get HIV that way unless he has open sores on his skin (in which case you probably wouldn't be kissing him there) and you had open sores in your mouth (ditto). If you know your partner well enough to kiss the shaft of his penis, I would think you might feel comfortable inquiring about his health status. Maybe it comes down to trust issues?
The best suggestions I can offer is to work on improving communication with him, and maybe both of you get exams anything seems wrong or questionable.
Otherwise, keep kissing and worry less!