This is a very good and important question, not only for you but for other people as well.
As people have said in the comments, YES it can be potentially dangerous to have unprotected sexual encounters with her without having tested for STDs first. Even if she's had unprotected sex with only ONE person, she would've been at risk for an STD.
As long as she ...
Assuming that we are talking about the risk of having intercourse one time under the conditions you described, and assuming you do not know if your male partner had an STD, and provided your partner used a latex or polyurethane condom labeled as protective against disease, the risk of contracting HIV, gonorrhea, chlamydia, and trichomoniasis quite low (it is ...
You can get Genital Herpes from someone licking your scrotum and there is no protection from Genital Herpes with condoms anyway as they don't cover the scrotum.
With oral sex, the risk is only there for you if the person giving oral sex has a cold sore and the risk is only there for your partner if you have Genital Herpes.
I'm afraid the answer is no, you can't know in advance if the condom is going to break.
As far as I can tell, and from my own personal experience, most condom failures are not due to the condom itself being bad, but from misusing it, e.g. putting it in a wrong angle (so it slides off during the act), using too much force during the act, thus tearing the ...
The pill slightly more effective than condom for contraception. Other methods are better still.
The pill is ineffective for preventing STI; condoms are mostly effective.
First things first. Statistics on contraception efficacy are widely available, so as a bonus you are getting info on several more types than just 'condom' and 'pill'.