What are the chances of catching an STD during unprotected?

[niceguy27!!]

I'm not being crazy hear 0.5% of the population so 1 in every 200 people has hiv in the UK. But if you sleep with someone who has hiv you only have a 3-9 in 10000 chance of catching it off the infected person. I thought if bb someone with an stdio/sti you were certain to catch it off them. I've always fantasised about going bb with an escorts I'd probably never do it though unless it was the day after her test results and all was clean. Let's be honest it is nicer without but I'd only do it with a long-term gf bb.