connect users to Custom post types

I suggest you to save it on user entity. Use update_user_meta() and stock it as an array. In this case if you delete an user, all associates info will be delete too.

<?php
$user_id = get_current_user_id();
$user_events = get_user_meta($user_id, 'user_events', true);
$user_events[$event_id] = $event_id; //you can also stock more infos, i use event_id as key to don't have duplicate event by user
update_user_meta($user_id, 'user_events', $user_events);
?>

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