There isn’t that much sex in the books themselves, and very little is explicit, mainly just what is implied.
His stuff is not as squeaky clean as Tolkien, but its nowhere near what HBO did with it.
Martins characters are very, very flawed, by design.
I will take your word for it, as I am judging by what I have seen on HBO.
If what you say is true, than HBO is doing a grave disservice to the author by changing the entire tone of the work.