Doctors go to school and residency for many years. Particularly since the 80s, they have seen a lot and learned to react with almost everyone. As everyone has said above, you would be doing yourself a grave disservice if you do not tell your internist if you are gay. If you are in a big or bigger city that will give him/her info he will be glad to have, particularly if you want to have blood test taken so that you can be informed about your HIV status. Ideally if you are sexually active and on PrEP you should be having blood tests. At any rate I think it will get you and your doctor off to a nice start if you are totally honest with him/her. And I think he/she will feel good that you can be honest with them.