Well there are biological factors and some sex acts are more risky, and some partners are necessary for those risky sex acts. That's why people will never stop thinking getting HIV depends on who your partner is.
From a cellular biology point of view, you're most likely to get HIV if you get buttfucked by a male infected partner who blows a load in your ass.
Transmission when an infected male blows a load in your vagina is way more rare. Transmission from infected vagina to non-infected penis is almost unheard of according to the CDC. Any open sore increases the risk of course.
Of course it's not PC to mention biological facts these days and maybe people will call it homophobic. Here's an article that gets more into this topic.
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