InvitationMailer.php

<?php

class InvitationMailer
{
  private $mailer;
  
  public function __construct(Mailer $mailer)
  {
    $this->mailer = $mailer;
  }
  
  public function sendInvitation(User $inviter, $invitee)
  {
    $this->mailer->send('emails.invitation', ['inviter' => $inviter], function($m) use ($invitee) {
      $m->to($invitee)->subject('You have been invited to this awesome app');
    });
  }
}

InvitationsController.php

<?php

class InvitationsController extends Controller
{
  public function store(InvitationMailer $mailer)
  {
    $user = auth()->user();
    $invitee = request()->get('invitee');
    
    $user->invite($mailer, $invitee);
  }
}

Invite.php

<?php

class Invite extends Model
{
  protected $fillable = ['invitee'];
  
  public function inviter()
  {
    return $this->belongsTo(User::class);
  }
}

User.php

<?php

class User extends Model
{
  public function invites()
  {
    return $this->hasMany(Invite::class, 'inviter_id');
  }
  
  public function invite(InvitationMailer $invitation, $invitee)
  {
    $invitation->sendInvitation($this, $invitee);
    
    return $this->invites()->create([
      'invitee' => $invitee
    ]);
  }
}