I'd definitely use separate lookup tables for user_event and user_highlight. Unless there is good reason to create a user_id|event_id|highlight_id relation (row), then it makes little sense to define it that way.
events
+-----+
event_id
detail
highlights
+---------+
highlight_id
detail
users
+----+
user_id
user_event
+---------+
user_id (FK)
event_id (FK)
user_highlight
+-------------+
user_id (FK)
highlight_id (FK)