So some other points.
Some Sex lubes can make it easier for infections to get into the body.
https://en.wikipedia.org/wiki/Personal_lubricant#Water-based
Thing is I wonder if a higher vitamin A and zinc intake can help because all epithelial cells need retinol (vitamin A), zinc is needed to move retinol around the body as Retinol Binding Protein (RBP) for epithelial cells. Alcohol can reduce fat soluble vitamins stored in the liver which can then reduce the VitA stored in the liver, you see this most easily with alcoholics and hypovitaminosis A, but even short term binge drinking can reduce levels enough to increase risks of transmission which probably explains man flu!
I found a cadaver study where they measured vitA content in the livers of dead people but didnt say how they died, knowing that you can die from ingesting too much vitA in one go like some arctic explorers did when eating polar bear livers decades ago and died. In order to get the highest amounts of vitA seen in some of these cadavers, you'd have to consume 30,000ui of VitA every day for at least a year without your body using any! Thats a lot of Vit A!!!
Anyone who paid attention to the Ebola outbreak in Africa a few years back, may remember that some viruses like Ebola can hide in parts of the body where the immune system can not go, namely the eyes and the testes and sometimes the brain, so they may have remembered that blokes testing negative for Ebola but previously had it, could still be passing it on through semen.
The thing with HIV, its typically passed through anal intercourse, not vaginal where there is sufficient lubrication, but its passed more frequently in Africa because they have a tendancy to have dry vaginal intercourse, because they actually try to reduce the wetness of the vagina which then creates microtears and sores and then its easy for HIV to get into the bloodstream, just like cuts and sores in the mouth also making it easy for HIV to get into the blood.
The whole 80's govt advice/warnings on HIV were directed at everyone because they didnt want to stigmatise those engaging in non vaginal intercourse.
The biggest risk from HIV is getting it into the blood, like most things which are pathogenic.
Now you can still have a highly effective immune system which can lock down viruses, but there is always the risk it gets into those parts of a body where the immune system cant go and I dont know what they test now a days.