I'm almost sure I read it in english, in a collection, more than 40 years ago. It was just possibly a shortish novelette, probably a short-story.
A plague has decimated mankind. Even though a cure did exist, only a single man managed to get access to it before everybody else was killed. He still has occasional fits of paralysis, prelude to death, but since the amount of medicine he has access to is huge, meant for a whole city, he can inject it over and over for his life-time and more.
The only other survivor was a woman who happened to be immune. The man wants to restart the human species. He hopes their future children can get the cure for long enough that eventually the plague will be definitely eliminated.
But he has to convince the woman. And she is very puritan. She wants a big marriage before starting a family. His arguments that there could be no priest or pastor to marry them leaves her undeterred : he can perform the rites himself, but she wants a white dress, flowers, and so on. So he manages to get all she wants, and they are about to enter together the big empty church. At the last minute, he has a pressing biological need. And since he is wearing a tuxedo, no pockets, he does not carry with him the medicine to inject in case of crisis.
Once in the toilet, he has a sudden attack of paralysis. He cannot get out but he can still call. The woman is within hearing distance, she knows where the medicine is, she has the skill to inject him, there is still time before paralysis kills him. The door to the toilets is not locked.
But he knows he is going to die, and mankind will not survive.
He is in the men's toilets. She won't get in.