adding relationship field

Hi , 

I have two modules. admb_partner and contacts. Between them exists an one to many relationship. I would like to create a checkbox field on the relationship. I looked to the opportunity role functionality but I can't seem to get it to work properly for my usecase

I have the current files in place:

custom/Extension/modules/Contacts/Ext/Vardefs/sugarfield_admb_partner_contact_main_mandatory_c.php

$dictionary['Contact']['fields']['admb_partner_contact_main_mandatory_c'] = array(
    'name' => 'admb_partner_contact_main_mandatory_c',
    'type' => 'bool',
    'source'=> 'non-db',
    'vname' => 'LBL_ADMB_PARTNER_CONTACT_MAIN_MANDATORY_C',
    'link' => 'admb_partner_contacts',
    'rname_link' => 'admb_partner_contact_main_mandatory_c',
    'massupdate' => false
);

www/custom/metadata/admb_partner_contactsMetaData.php

<?php
// created: 2018-01-03 16:24:52
$dictionary["admb_partner_contacts"] = array (
  'true_relationship_type' => 'one-to-many',
  'relationships' => 
  array (
    'admb_partner_contacts' => 
    array (
      'lhs_module' => 'ADMB_Partner',
      'lhs_table' => 'admb_partner',
      'lhs_key' => 'id',
      'rhs_module' => 'Contacts',
      'rhs_table' => 'contacts',
      'rhs_key' => 'id',
      'relationship_type' => 'many-to-many',
      'join_table' => 'admb_partner_contacts_c',
      'join_key_lhs' => 'admb_partner_contactsadmb_partner_ida',
      'join_key_rhs' => 'admb_partner_contactscontacts_idb',
        'rel_fields' => array(
            'admb_partner_contact_main_mandatory_c' => array(
                'type' => 'bool',
                'default'=> 0,
            )
        )
    ),
  ),
  'table' => 'admb_partner_contacts_c',
  'fields' => 
  array (
    'id' => 
    array (
      'name' => 'id',
      'type' => 'id',
    ),
    'date_modified' => 
    array (
      'name' => 'date_modified',
      'type' => 'datetime',
    ),
    'deleted' => 
    array (
      'name' => 'deleted',
      'type' => 'bool',
      'default' => 0,
    ),
    'admb_partner_contactsadmb_partner_ida' => 
    array (
      'name' => 'admb_partner_contactsadmb_partner_ida',
      'type' => 'id',
    ),
    'admb_partner_contactscontacts_idb' => 
    array (
      'name' => 'admb_partner_contactscontacts_idb',
      'type' => 'id',
    ),
    'admb_partner_contact_main_mandatory_c'=>
    array (
        'name' => 'admb_partner_contact_main_mandatory_c',
        'type' => 'bool',
        'studio' => false,
        'source' => 'non-db',
        'vname' => 'LBL_ADMB_PARTNER_CONTACT_MAIN_MANDATORY_C',
        'rname_link' => 'admb_partner_contact_main_mandatory_c',
        'default' => 0,

    )
  ),
  'indices' => 
  array (
    0 => 
    array (
      'name' => 'idx_admb_partner_contacts_pk',
      'type' => 'primary',
      'fields' => 
      array (
        0 => 'id',
      ),
    ),
    1 => 
    array (
      'name' => 'idx_admb_partner_contacts_ida1_deleted',
      'type' => 'index',
      'fields' => 
      array (
        0 => 'admb_partner_contactsadmb_partner_ida',
        1 => 'deleted',
      ),
    ),
    2 => 
    array (
      'name' => 'idx_admb_partner_contacts_idb2_deleted',
      'type' => 'index',
      'fields' => 
      array (
        0 => 'admb_partner_contactscontacts_idb',
        1 => 'deleted',
      ),
    ),
    3 => 
    array (
      'name' => 'admb_partner_contacts_alt',
      'type' => 'alternate_key',
      'fields' => 
      array (
        0 => 'admb_partner_contactscontacts_idb',
      ),
    ),
  ),
);

When I now repair and rebuild I would expect an update on the relationship tabel. This didn't happen.But when I open a partner I do get an mysql error that says that the field is not found on the relationshp table. So i added myself to the tabel using alter query. After I added the specified field to the override subpanel using the following entry in the fields list I can see the field in the subpanel but any changed made are not saved so it seems. But when I add the value in the database directly the value is read and displayed correctly. So the big question is.. What am I missing?

          3 =>
        array (
          'name' => 'admb_partner_contact_main_mandatory_c',
          'label' => 'LBL_MAIN_MANDATORY',
          'enabled' => true,
          'default' => true,
        ),

Also another question is, is it possibel to overwrite/enhnce the accounts_contacts relationship with a custom field?