Year 12s: what will be the first way you research your future options? >>

Question about sexual relationships and sti's..

I'm sure I'm missing something obvious here but after all these years I'm having to ask this. How can you reliably know that you are not going to get an sti in a relationship? The obvious answers seems to be to get tested but most people don't seem to do this. Of those that do results are usually given over the phone to the partner so you are still trusting what they tell you. Even then some sti's like hiv don't show up on tests for several months after catching them. There's condoms but many girls are on the pill and don't use them.

How do most people trust that who they are sleeping with is sti free?