Y luego si te he visto no me acuerdo

Y luego si te he visto no me acuerdo
 

in English?

se usa en contextos sexuales, cuando hacemos algo y luego pasamos del tema.

Literally, it means "If I've seen you (before), I don't remember."
This can be also be said, "Have we met?"

But, the modismo means more than that. It's like saying you'd rather not remember, or you don't want to let on that you know each other. Is that right?

There are some things you can say when you want to ignore a topic that comes up, such as "We'll just ignore that" or "We'll just pretend that never came up".

Bueno normalmente se usa en ocasiones de one night stand, o algo así. SOmething like It was just a night stand.

Hmmm, can you use it in a sentence? That way I can try to translate the whole sentence.

Mi amigo Fernado es de los que ligan mucho los fines de semana, se las folla y luego si te he visto no me acuerdo.