firebase return

I would like help with the return of firebase, this is the following, in my angular project I have a component with some fields to validate and a validation-only service, I am having difficulty getting a return as I need it, follow the code

My form.ts component I have:

nextPage() {
if(this.serviceValidate.validaEmail(this.dataForm.value.gn_email)) {
   return;
 }
}

In my validation service I have ValidaUsuario.service.ts I have:

  validaEmail(email: string): any {
let valida = /^[a-zA-Z0-9][a-zA-Z0-9\._-]+@([a-zA-Z0-9\._-]+\.)[a-zA-Z-0-9]{2,3}$/;
 //1º validação
if(email == '') {
  this.snackbar.openSnackBar('Campo email obrigatório');
  return false;

//2º validação
} else if(!valida.exec(email)) {
  this.snackbar.openSnackBar('Email não é valido, tento outro!');
  return false;
} 

// 3º validação
 var data =  this.db.list(this.PATH,
 ref => ref.orderByChild('gn_email')
           .equalTo(email))
           .valueChanges(); 
}

If possible, I would like to get a boolean in this 3rd validation, I already tested two ways so

var data =  this.db.list(this.PATH,
    ref => ref.orderByChild('gn_email')
               .equalTo(email))
               .valueChanges();

and so:

   firebase.database().ref(this.PATH)
 .ref.orderByChild('gn_email')
 .equalTo(email)
 .on('child_added', function(snapshot) {
   console.log(snapshot.exists())
   var data = snapshot.exists();
// })

How to get the return without doing the subscribe in the component?