Your lover has a grounding influence on your emotions. When you're feeling upset or stressed out, they are able to step in with some well-worded advice and comfort. When you're flying high and maybe getting a little bit unrealistic in your ideas or expectations, they are able to provide a more realistic view of the possibilities.
Don't misunderstand -- this isn't a limiting aspect to your relationship. In fact, it is one that really helps you feel secure and well-loved. After all, a big part of feeling loved is feeling both understood and encouraged, and that is what this person offers you, as long as you're communicating well. Instead of taking your mutual good feelings for granted, you should both take care that you always make a conscious effort to talk things over, tell your partner how you're feeling, listen to how they're feeling and so on. This shouldn't be very hard; you really respect and trust each other, which helps both of you feel comfortable in being honest and straightforward about your emotions, point of view and so on. This kind of aspect is a wonderful influence in a love relationship, but it's also great for business -- so if you two have ideas about launching a project together, you can feel reasonably assured that it'll work out well!