Directive disappears when cancel button is pressed

Question

I need to validate a date, so I create a directive validators:

@Directive({
  selector: ' input[id=datanint]',
  providers: [{
    provide: NG_VALIDATORS, useExisting: DateValidatorDirective, multi: true
  }]
})
export class DateValidatorDirective implements Validators {
  private regExp = /^(0?[1-9]|[12][0-9]|3[01])[\/](0?[1-9]|1[012])[\/]\d{4}$/;

  validator: ValidatorFn;

  constructor(private el: ElementRef) {
    this.validator = validateregex();
  }

  validate(c: FormControl) {
    if (this.el != null && this.el.nativeElement.value != null && this.el.nativeElement.value != '') {
      if (!this.el.nativeElement.value.match(this.regExp)) {
        return this.validator(c);
      }
    }
  }
}

function validateregex(): ValidatorFn {
  return (c: AbstractControl) => {
    return { pattern: true }

  }
}

This is my HTML markup:

<mat-form-field>
    <input id="datanint" formControlName="date"  matInput [matDatepicker]="picker" />
    <mat-datepicker-toggle matSuffix [for]="picker"></mat-datepicker-toggle>
    <mat-datepicker #picker startView="multi-year"></mat-datepicker>
</mat-form-field>

And my Typescript where I create a form builder:

function initializeForm() {
     const valObject = {
                            date: [],
                            name:[Validators.required]
        ...
            }
             Object.keys(fg.controls).forEach(key => {
                        const control = fg.get(key);
                        if (valObject[key] && key!="date") control.setValidators(valObject[key]);
                        else {
                            if( key!="date"){
                             control.clearValidators();
                            }
                           
                        }
                    });
    }

The program works until I add a new date and I get the correct error messages, but when I click cancel button and I do :

form.reset();
initializeForm()

The error message disappears, it seems like the validator on the date is deleted, but this is impossible because the validator is linked to directive.

Can anyone help me?