I stopped counting a solid decade ago. It got embarrassing when my mental list started including names like "grocery store guy" and "the time I took one for the team with Amy." Something like 2-10 a year for 20 years. I'd guess in the neighborhood of a hundred.
God, who knows. Since my divorce in 2004, at which point I dived into the bi lifestyle, I count somewhere around 30. I was sexually active for 32 years before 2004, and spent a decade playing in a rock band and fucking every girl I could, so, I don't know, 80 - 90 maybe - and I have never once in my life had any kind of STD.
I've never counted them all up and wrote it down, I try to in my head, sometimes i forget a few or remember a few everytime this question comes up, if I had to guess, probably high teens , perhaps lower 20's. but high teens seems about right.