In general, with the verb aimer, the more you add, the more you are watering it down. So j'aime is stronger then j'aime bien. So that's why you would say je t'aime to a romantic interest and never je t'aime bien J'aime means I like, but j'aime bien means you like, but not as intensely, like you think it's not bad.

As Sufia has explained. Aimer means to love, but aimer bien just means to like.