I tend to create separate tables for likes and comments. I usually create this sort of schema:
Likes
-----
id // autoincrement
obj // the related model (the name of the model that is being liked)
obj_id // the foreign key
user_id // the user id that liked the model object
created // timestamp
updated // timestamp
Then the comments table:
Comments
--------
id // autoincrement
obj // the related model (same as above)
obj_id // the foreign key
message // the comment itself
user_id // the user id that commented on the model object
created // timestamp
updated // timestamp