goalText: string = 'Это моя новая запись';
commentText = ['Это мой новый комментарий'];
goals: string[];
comments = ['Первый'];
arrcom = [this.goals, this.comments];
    ngOnInit() {
    this._data.goal.subscribe(res => this.goals = res);
    this.itemCount = this.goals.length;
    this._data.changeGoal(this.goals);
    this.comcount = this.comments.length;
    }
  addItem() {
    this.goals.push(this.goalText);
    this.goalText = '';
    this._data.changeGoal(this.goals);
    this.itemCount = this.goals.length;
  }
  addComment(i) {
    this.arrcom[i].push(this.commentText[i]);
    this.commentText[i] = 'Комментарий';
    this.comcount = this.arrcom[i].length;
  }

<div class="container color-light" [@goals]="goals.length">
  <div class="col">
    <p class="sm">Форма для ввода записи</p>
    <form>
      <input type="text" class="txt" name="item" placeholder="Введите Вашу запись здесь" [(ngModel)]="goalText" />

      <input type="submit" class="btn" [value]="btnText" (click)="addItem()" />

    </form>
  </div>
  <div class="col">
    <!--  -->
    <div ng-scroller>
      <div class="life-container"  *ngFor="let goal of goals, let i = index" [attr.data-n]="i">
        <p>
          {{i+1}}) {{ goal }}
        </p>

        <form class="commentarii">

          <input type="text" class="txtcomment" name="item" placeholder="Ваш комментарий" [(ngModel)]="commentText[i]" />
          <input type="submit" class="btnComment" [value]="btnCommentText" (click)="addComment(i)" />
        </form>
        <p class="life-container-com" *ngFor="  let comment of arrcom[i], let j = index,">
          {{ comment }}
        </p>
      </div>

    </div>
  </div>
</div>