A relationship (a good, healthy one) should give you a sense of purpose, pride, and feeling of growth. You need to feel that you are becoming a better person solely because of the fact that you are in the relationship. You should feel that the moments you are spending with your partner are worthy of your energy and that you are becoming a bigger person because of all that.
In order to be stimulating, a relationship needs to offer you quality time - quantity (meaning spending a lot of time together) does not mean anything on its own. In fact, it has been said that people that spend too much time together without doing anything interesting eventually drift apart, due to not feeling any kind of positive emotions while being together.