Strawberry mousse with pistache cream inside, the Saya by Sadaharu Aoki is my favourite cake. Sadaharu Aoki have two patisseries in Paris, 35 Rue de Vaugirard near the Luxembourg park, and 56 Boulevard de Port Royal in the 5 arrondissement.
If you need somewhere to contemplate leaving your lover, go alone, and if you don't mind them not being there to share something sublime in a glass or a dish, you have your answer.