Why does it take millions of ejaculated sperm to fertilize one egg?

If one masturbates but does not get involved in any other sexual activities, is that person considered to be sexually active?

If my husband takes antivirals or post-exposure prophylaxis can we still have sex with a condom and still complete the process like normal? It is affecting our sex life because he does not want to infect me. I don't want to be infected but I knew what I was getting into from the start. I might start PrEP as it is now available to me. What are your thoughts?

What is it that doctors are looking for in a urine test for STIs? How exactly do they test the urine for the various infections?

Thank you for your time and help.

I am a twenty-one-year-old virgin who has just recently started seeing a girl very seriously. I am frustrated at how my body reacts to the slightest physical stimulus. Holding hands, talking about physical affection, even thinking about kissing gives me an erection. I am not thinking about sex, and we are not going to have sex until we are married, but I can't believe how frequent these erections are. I know it's common for guys my age to have erections, but just being with a girl I care about gives me one, and it's not easy to hide, and I don't want her to think the wrong thing. I used to masturbate and view pornography a lot but I finally stopped because I didn't agree with it. I stopped about the same time I met her. Do you think that my past is causing my body to want something I'm not going to give it?

My boyfriend has suggested "tit sex" as an alternative to intercourse, which we want to wait a while to go ahead and do. I want to know, what exactly is "tit sex" and how do you do it? Will it hurt?