Welcome back to the Forum. I'll go straight to your questions:
1) I know hand-to-genital is safe. The breast-to-genital is safe too?
Yes, this is safe sex. Genital to breast contact is a form of masturbation.
2) When I lay prone on the bed, she sat on me. She was wearing her underwear all the time. But I was naked, so our butt contacted, any STDs will transmit by this way?
No this sort of touching and contact is not associated with STD transmission. There would not be any risk even if she were entirely naked.
3) When I turned over, i know I should tell her do not sit on me. But, before I said anything, she was sitting on me. Then I told her do not do it immediately, but it has been last about 10-15 seconds already. My penis touched her underwear, I was so nervous at that time, so I didn’t notice which area my penis touched, maybe the vagina area or the anal area. One thing I am pretty sure is she was wearing underwear, so there is no inserted action, just touched her leg and her underwear.if she had syphilis,genital warts or herpes just under her underwear,will it transmit?Will Hiv or any other STDs will transmit by this way?
Again, no risk at all, No penetration, no risk, with or without underwear.
4) I don’t know whether she is in period. If she is in period, although there is no inserted action, could the blood bleeding out from the underwear to increase the hiv risk?
No even if she were on her period there would be no risk.
5) I didn’t see any ulcer or genital warts on her leg, but if she had ,will herpes, genital warts and syphilis be transmitted by the very short contact?
Nope, still no risk.
i have read this topic, and I think we are similar. Dr. hhh said it has little or no risk. Should I think there is no risk at all?
I agree with my colleague Dr. Handsfield. This sort of exposure has no meaningful risk for STD acquisition, including HIV.
I hope my comments are helpful. EWH