As far as I know, this is not a word in English. Or if it is, then it's not a common one. Maybe someone else has heard it.

Perhaps you could say that they're 'in a casual relationship'? This means that they go out together sometimes, but haven't made any kind of commitment. By the way, you confused us all by saying ' I'm looking for meaning of "vacile" in English' . This word has no meaning in English because it's not an English word! You should have said something like 'I'm looking for a translation of ..' or 'I want to know how to say ... in English'.

This word doesn't exist in English, at least at the moment. It's an existing word in Spanish, but with a completely different meaning.