Is transmission of sexually transmitted infections and HIV also possible if the man only penetrates the vagina for a very short time?

Yes. Without a condom, even brief penetration of the penis into the vagina can lead to infection with sexually transmitted infections or HIV.

Is the transmission of infections possible even if there has been no orgasm?

Yes. Unprotected vaginal sex is a risk even without ejaculation. Infection occurs through the mucous membranes.

Can I also be infected in a committed partnership?

Yes. As long as you are not both tested for HIV or sexually transmitted infections, you do not know if you are protected. HIV or other sexually transmitted infections such as chlamydia can be carried for several years even without symptoms. Important: Whether married or not, flings can happen in a committed relationship. So, if you have a one-night stand or an affair, always use a condom – and thus protect yourself and your partner.