Professional writers write about stuff they don't have firsthand experience doing all the time. Whether it's killing someone, or cooking, or rock climbing, or... yes, sex. How do they do this? They do research.

Yes, someone who has firsthand experience with cooking or rock climbing or sex (or killing, I guess, but...) might then send this author a letter saying, "hey, you got x, y, and z wrong," no matter how much research they did. It happens. This is a hazard of doing writing.

I once did a thread with someone where our characters were making chocolate. I don't know shit about making chocolate because I have never done it before. Other player obviously had a better idea of what they were doing. Did the thread suddenly collapse because I might have gotten some details wrong and had to fudge it with internet research? No. Why? It didn't matter. We're two people writing about fictional characters making fictional chocolate. It doesn't have to be perfect.

tl;dr your smut thread is not going to be perfectly accurate no matter how much research you do or porn you watch, and that's okay.